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Speaker 1: Hey, welcome to side Stuff, a production nuff iHeartRadio. I'm

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Speaker 1: Hoory Champ, and today we are taking a crack at

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Speaker 1: knuckle cracking. Why do we do it, why does it happen?

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Speaker 1: And is it bad for you? We're going to talk

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Speaker 1: to a couple of experts about it, including one researcher

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Speaker 1: who thinks they figured out the real reason why joins

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Speaker 1: made that popping sound. It's not what you think, So

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Speaker 1: stop wringing your hands, get cracking with us as we

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Speaker 1: snap up and answer to the question why do our

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Speaker 1: knuckles crack?

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Speaker 2: Hey?

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Speaker 1: Everyone, So, one of the fun things about being a

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Speaker 1: current is seeing something about yourself end up in your kids.

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Speaker 1: It could be your looks, or your personality or even

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Speaker 1: your mannerisms. It's usually fun, but sometimes can be a

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Speaker 1: little unsettling. Cannot a minute, WHOA, I'm talking me correctly. Yes,

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Speaker 1: I am a knuckle cracker, and so is my daughter,

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Speaker 1: but my spouse and my son not so much, which

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Speaker 1: made me wonder why do some people's knuckles crack and

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Speaker 1: some don't? What actually makes that sound? And is it

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Speaker 1: bad for you? And if it is bad, why do

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Speaker 1: we keep doing it? As it turns out, knuckle cracking

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Speaker 1: has to do with the type of joint we have

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Speaker 1: in our bodies. To tell us about this type of joint,

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Speaker 1: I reached out to doctor Neilima Sharma, a biologist and

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Speaker 1: researcher at University College London. Well, thank you so much,

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Speaker 1: Taka Sharma for joining us.

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Speaker 2: Sure, that's my pleasure.

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Speaker 1: Today we're talking about knuckle cracking and here it has

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Speaker 1: something to do with something called a sinovial joint. Is

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Speaker 1: that how you pronounce this iino you' or sinovio?

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Speaker 2: I guess it may depend on whether you're on the

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Speaker 2: side of the Atlantic.

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Speaker 1: How do you pronounce it?

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Speaker 2: I call it a synovial joint?

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Speaker 1: Syno jo. We'll go with them. Can you tell us

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Speaker 1: what is the sinovial joint?

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Speaker 2: So, sinobal joints are the kind of joints that are

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Speaker 2: found in your elbow or your hip. They are characterized

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Speaker 2: by relative sliding of two surfaces next to each other. So,

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Speaker 2: if you want a common example, a door hinge functions

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Speaker 2: very similar to how a cynobial join functions. You have

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Speaker 2: two metal surfaces in a door hinge that are sliding

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Speaker 2: with respect to each other.

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Speaker 1: So most of the joints in your body are what

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Speaker 1: are called sinobial joints or synovial joints as other people

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Speaker 1: pronounce it, And those are the kinds of joints that

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Speaker 1: are like door hinges or like ball of socket joints,

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Speaker 1: where the surface of one bone curves around the surface

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Speaker 1: of the other bone, and they rotate and slide around

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Speaker 1: each other. That's one way to join two boats together.

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Speaker 1: Another kind of joint that you see in nature and

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Speaker 1: in some parts of our body are cartilaginous joints.

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Speaker 2: So these are the joints found in your spine. So

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Speaker 2: here you have two bony elements which are very stiff,

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Speaker 2: and they are connected by a soft cartilage element in

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Speaker 2: the middle. Okay, so you can imagine, like the way

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Speaker 2: they function is by bending.

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Speaker 1: So this kind of join cartilaginous joint don't have any

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Speaker 1: moving parts. It's basically like joining the ends of two

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Speaker 1: sticks of wood together with a short rubber tube. The

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Speaker 1: joint bends by bending the tube. Now, when we were

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Speaker 1: evolving as primitive animals, we first evolved bones and cartilage,

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Speaker 1: and initially all of our joints were cartilaginous. You can

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Speaker 1: imagine we were blobby fish swimming in the ocean and

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Speaker 1: we had a skeleton, but it was all put together

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Speaker 1: with basically rubber joints. But then at some point we

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Speaker 1: started developing this new kind of joint, synovial joint, which

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Speaker 1: had two moving, rotating parts. Now, if you have two

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Speaker 1: bones rotating and rubbing against each other, after a while,

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Speaker 1: they'll wear each other out and get creaky. So a

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Speaker 1: feature of these sinovial joints is that they have a

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Speaker 1: gap in between the two bones which is filled with

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Speaker 1: a lubricant.

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Speaker 2: And again, like an adore hinge, you need to keep

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Speaker 2: the joint lubricated, so you oil these hinges very often

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Speaker 2: to maintain a seamless function. In the same way, our

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Speaker 2: sinoval joints are also highly lubricated.

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Speaker 1: I see, I'm not very handy around the house, so

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Speaker 1: I don't really lubricate my hinges, maybe as much as

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Speaker 1: I should. But what's special about a sainovial joint as

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Speaker 1: opposed to any other kinds of joints.

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Speaker 2: So this substance called sinovial fluet, which exists between these

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Speaker 2: two surfaces that gives our sinoval joints that's lubricating properties.

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Speaker 1: So snovial joints have a gap between the two surfaces

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Speaker 1: of the bones that slide past each other, and this

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Speaker 1: gap is filled with a special liquid that is basically

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Speaker 1: like a super lubricate.

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Speaker 2: So this is a very cool fact about sinoval sewage.

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Speaker 2: Particularly the sinoval fluid, is a substance that is known

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Speaker 2: to have one of the lowest coefficient of friction in

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Speaker 2: both biological materials as well as engineered materials.

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Speaker 1: Really, it's super slippery.

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Speaker 2: Yeah, it's super slippery. It's more slippery than what ice

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Speaker 2: on ice feels like. Really, and ice on ice is

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Speaker 2: super slippery. Yeah, whoah, more slippery than oil. Yeah, absolutely,

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Speaker 2: And that's why you have to lubricate your door headges

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Speaker 2: get a few months now.

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Speaker 1: You're making me feel guilty, But.

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Speaker 2: You do not have to lubricate your joints as much.

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Speaker 2: They function for sixty years of age if you take

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Speaker 2: care of them properly.

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Speaker 1: Now, these special sinovial joints with the two bones separated

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Speaker 1: by gap filled with a super slippery liquid are basically

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Speaker 1: the reason our knuckles crack. We'll get into the physics

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Speaker 1: of why that happens later in the program. But what

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Speaker 1: this type of joint also did is give our vertebrate

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Speaker 1: ancestors essentially a superpower.

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Speaker 2: This kind of joint. So you can imagine that when

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Speaker 2: I'm moving my elbow, I do not really face a

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Speaker 2: resistance while I'm moving it. So it's I know, will

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Speaker 2: joints allow you to be more mobile and faster. I

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Speaker 2: can move my elbow so much faster because there's absolutely

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Speaker 2: no resistance here and all I have to do is

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Speaker 2: turn my muscle on. This would have allowed animals to

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Speaker 2: operate quickly. So if I'm a predator and I have

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Speaker 2: a joint that moves early fast, I am definitely able

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Speaker 2: to cash more prey and I'm also able to evade predators.

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Speaker 2: So they must definitely have given animals and edge over

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Speaker 2: other animals who did not have these joints. And maybe

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Speaker 2: that's why they spread so fast that most vertebrates that

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Speaker 2: we'd know now do have a lot of signe joints.

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Speaker 1: Oh, that could have been their secret weapon to take

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Speaker 1: over the world.

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Speaker 2: Yeah, absolutely, WHOA, this is your speculation, but definitely interesting speculation.

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Speaker 1: Yes, so sygnobil joints could possibly be the reason you, me,

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Speaker 1: and most vertebrate animals are here. Cinovial joints are easier

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Speaker 1: to move and therefore faster, and they have a wider

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Speaker 1: range of motion than the cartilaginous type of joint, which

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Speaker 1: could have given the vertebrates that had sinobial joints the advantage.

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Speaker 1: Now it's interesting to think about what exactly prompted vertebrates

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Speaker 1: to develop this type of joint. According to doctor Sharma,

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Speaker 1: the conventional wisdom for at least the last hundred years

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Speaker 1: or so has been that vertebrates evolved this kind of

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Speaker 1: joint when they moved from the ocean to land. The

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Speaker 1: idea is that sinovial joints are better for standing and walking.

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Speaker 2: People used to think that cinobil joints only evolved because

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Speaker 2: animals moved out from water to land, and because on

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Speaker 2: land you have to bear larger loads. You need like

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Speaker 2: these joints which do not become unstable.

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Speaker 1: Because cartilaginist joints are unstable.

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Speaker 2: Because they are like a rubber tube. Now, if I

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Speaker 2: stand on a rubber tube, it can compress or it

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Speaker 2: can buckle out of shape.

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Speaker 1: I see.

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Speaker 2: It's not that sinovil joints don't become unstable, but they

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Speaker 2: are definitely more stable than cartilaginous joints. If you would

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Speaker 2: want similar range of motion out of the two joints,

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Speaker 2: so there was a conventional wisdom for many years we

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Speaker 2: have cygnovial joints because we needed them to walk on land.

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Speaker 2: But the reason I reached out to doctor Sharma is

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Speaker 2: that she's the lead author in a recent study that

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Speaker 2: says this is not true.

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Speaker 1: So this is a paper.

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Speaker 2: In fact, I was published last year, and I was

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Speaker 2: researching the question of when the joints evolved, whether or

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Speaker 2: not skates and sharks at sinobile joints.

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Speaker 1: What doctor Sharma and her colleagues did, by study current

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Speaker 1: animals and studying the fossils of ancient animals, was to

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Speaker 1: sort of pinpoint the evolution of sinovial joints and therefore

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Speaker 1: when exactly animals started to be able to possibly start

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Speaker 1: cracking their knuckles. And they dated it to about four

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Speaker 1: hundred million years ago. Now this date is significant according

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Speaker 1: to doctor Sharma for two reasons. And they're going with

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Speaker 1: me here for a second. I promise it'll be worth it.

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Speaker 1: That date four hundred million years ago is before animals

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Speaker 1: moved from the ocean to land. So the reason we

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Speaker 1: have synovial joints is not so we could stand up.

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Speaker 1: But wait, if that's not the reason, then what is well,

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Speaker 1: four hundred million years ago. It's also the time when

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Speaker 1: jaws were first developed. That's right, before four hundred million

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Speaker 1: years ago, fishes just kind of had a circular mouth,

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Speaker 1: sort of like lampreeze or leeches. But then four hundred

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Speaker 1: million years ago, vertebrates evolved jaws that could open and close,

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Speaker 1: and that could bite and chomp and prey. And this

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Speaker 1: brings up the crazy idea that maybe the reason we

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Speaker 1: evolved synovial joints, and therefore the reason we can crack

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Speaker 1: our knuckles, could have been to eat better. Okay, to

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Speaker 1: be fair, the evolution of sinnovial joints and the evolution

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Speaker 1: of jaws happening at the same time could just be

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Speaker 1: a coincidence, and there are sort of examples of old

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Speaker 1: fish that maybe have sinobial joints in their fins and

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Speaker 1: not their jaws. But still it does point to one

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Speaker 1: possible answer to the question why do we crack our knuckles.

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Speaker 1: Here's my hypothesis that knuckle cracking is a byproduct of

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Speaker 1: developing these kinds of joints so that we could move

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Speaker 1: faster and be better at eating and moving and running

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Speaker 1: and swimming, and eventually walking and running it's like it's

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Speaker 1: something we can't avoid if we wanted to have this

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Speaker 1: kind of joint.

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Speaker 2: Yeah, I guess not. It is definitely a byproduct of

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Speaker 2: the evolution of these kind of joints and an interesting

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Speaker 2: vibe product.

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Speaker 1: In other words, if we couldn't crack our knuckles, we

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Speaker 1: probably wouldn't be here. Okay, I just had one more

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Speaker 1: question or doctor Sharma. Okay, last question, do Korsharma? Can

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Speaker 1: you crack your knuckles?

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Speaker 3: Yes?

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Speaker 1: Oh my goodness. Oh well, it's really loud.

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Speaker 2: To be honest, I don't think I've done this in

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Speaker 2: the last five years. Oh really, Yeah, I do have

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Speaker 2: because usually.

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Speaker 1: Oh, you have this ability to crack your knuckles, but

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Speaker 1: it's not a composion for you. No. That brings us

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Speaker 1: the next question we're going to answer in this episode,

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Speaker 1: which is, if we can crack our knuckles, why do

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Speaker 1: we do it? And why do some of us do

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Speaker 1: it compulsively? When we come back, I'm gonna talk Jane

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Speaker 1: neuroscientists about this, and we're gonna address whether cracking your

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Speaker 1: knuckles is that for you. So stay with us. We'll

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Speaker 1: be right cracked, but I mean we'll be right back. Hey,

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Speaker 1: we'll come back we're talking about cracking our knuckles, and

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Speaker 1: so far we've learned the reason we can crack our

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Speaker 1: knuckles is that it's a feature that came with an

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Speaker 1: upgrade in the joints of our early vertebrate ancestors. Those

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Speaker 1: are the joints in your body are what are called

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Speaker 1: sinovial or synovial joints, and they're pretty good. Here. Try this,

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Speaker 1: if you can swing your arms around in a circle

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Speaker 1: and open and close the fingers in your hand. Isn't

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Speaker 1: it incredible how easy and smooth it is to do that,

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Speaker 1: and be amazed at what a wide range of motion

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Speaker 1: each of your joints has. Well, it's all due to

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Speaker 1: signovial joints, but sometimes they do crack. We'll get to

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Speaker 1: the physics and the fluid dynamics of why that happens.

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Speaker 1: But first I thought we could answer the question of

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Speaker 1: why we crack our knuckles from a psychological point of view,

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Speaker 1: Why are we compelled to crack our knuckles and why

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Speaker 1: does it annoy certain people? To dig into the mind

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Speaker 1: of the knuckle cracker, I reached out to doctor Dwayne Godwin,

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Speaker 1: a psychologist and neuroscientist at Wake Forest University and the

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Speaker 1: co author with me of the book Out of Your Mind. Well,

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Speaker 1: thanks doctor Godwin for joining us again.

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Speaker 4: Hey or hey, how are you doing.

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Speaker 1: I'm great. I'm cracking my knuckles here.

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Speaker 4: Oh are you?

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Speaker 1: I can't stop. I can't stop. That's the that's the

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Speaker 1: question we're trying to answer today. Can you character knuckles?

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Speaker 1: You just don't do it. I can.

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Speaker 4: It's not very impressive.

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Speaker 1: Oh oh boy, that was pretty loud.

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Speaker 2: Yeah.

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Speaker 4: Oh it's a microphone.

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Speaker 1: The first thing I asked doctor Cockwin was what does

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Speaker 1: psychologists think of knuckle cracking? And apparently the answer is

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Speaker 1: they don't.

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Speaker 2: Yeah.

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Speaker 4: You know, there's not an extensive literature on knuckle cracking.

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Speaker 4: With a lot of the other things we talk about,

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Speaker 4: there's usually something like a study, there's scales that you

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Speaker 4: can compare with advanced neuroimagery. But knuckle cracking, you know,

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Speaker 4: it doesn't really hurt you for the most part. It

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Speaker 4: doesn't produce the kind of euphoria that you might associate

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Speaker 4: with a drug, so it's harder to study in that way.

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Speaker 1: I see, it's not high in the priority list of

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Speaker 1: the nih or National Science Foundation.

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Speaker 4: You know, if you're sort of balancing things out, Oh am,

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Speaker 4: I going to look at brain tumors versus knuckle cracking.

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Speaker 1: Yeah, but not everyone can study brain tomors. I mean,

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Speaker 1: somebody's got to study the knuckles. Yeah, So knuckle cracking

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Speaker 1: is not a high priority in the scientific community, although

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Speaker 1: we did find a couple of case reports where psychologists

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Speaker 1: have treated people who said they had a problem with

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Speaker 1: cracking their knuckles.

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Speaker 4: Yeah, there are a few case reports where this joint

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Speaker 4: cracking or clicking becomes excessive or distressing or really hard

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Speaker 4: to stop. One of the reports described compulsive joint clicking

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Speaker 4: driven by an uncomfortable joint sensation that they could ease

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Speaker 4: only after repeated clicking. So it would be like, you know,

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Speaker 4: popping your neck multiple times to get relief in your neck.

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Speaker 4: And then there was another case study that described improvement

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Speaker 4: with this dopamine drug and the fidget spinners.

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Speaker 1: Yes, you can take a drug to stop cracking your knuckles.

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Speaker 1: Look at to why that works in a little bit.

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Speaker 1: But first I wanted to ask doctor Godwin what he

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Speaker 1: thought was going on in the brain when we crack

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Speaker 1: our knuckles.

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Speaker 4: So it's not hard to reason out what might be happening.

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Speaker 4: A reasonable hypothesis is that knuckle cracking can ride along

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Speaker 4: on the same circus that the brain uses for habits

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Speaker 4: in our normal lives. The habit system is a feature

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Speaker 4: and not a bug. It takes actions that you repeat

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Speaker 4: a lot, makes them fast and low effort. You don't

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Speaker 4: want to consciously replan every step of tying your shoes

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Speaker 4: or unlocking your phone or driving a familiar route, and

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Speaker 4: so the brain chunks those behaviors into packages that can

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Speaker 4: run with minimal supervision.

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Speaker 1: I see, it's like the brain is made to put

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Speaker 1: certain things into that category of automatic behavior.

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Speaker 4: Yeah, it's very advantageous from an evolutionary perspective. If you

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Speaker 4: were thinking about every action that you took, then it

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Speaker 4: would be very difficult to navigate the world day to day,

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Speaker 4: and it would be difficult if you were performing at

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Speaker 4: a very high level in sports. For example, if you

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Speaker 4: had to think about every placement of a golf club

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Speaker 4: as you were making a swing. If you don't somehow

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Speaker 4: make that more automatic, then you get into issues like choking,

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Speaker 4: because that is kind of overthinking those kinds of behaviors.

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Speaker 1: In other words, our brain is wired to form habits,

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Speaker 1: and to form a habit, all you need is for

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Speaker 1: you to do it several times and for it to

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Speaker 1: feel good.

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Speaker 4: So early in learning, the prefrontal cortex is more involved

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Speaker 4: because you're deciding and evaluating. But with repetition, the control

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Speaker 4: shifts toward the dorsal strainum and motor planning areas and

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Speaker 4: the behavior becomes more automatic, and dopamine is involved in that.

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Speaker 4: It's one of the signals that helps to stamp in

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Speaker 4: a habit if it's producing either a rewarding outcome or

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Speaker 4: a relief, and relief in some sense can be rewarding

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Speaker 4: related to this sort of knuckle cracking behavior.

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Speaker 1: Like if it somehow feels good, then your brain will

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Speaker 1: want to keep doing it.

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Speaker 4: Yeah, for knuckle cracking, the rewards is kind of this

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Speaker 4: relief from stiffness or tension in the joint, and relief

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Speaker 4: can be powerful because it teaches the brain that this

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Speaker 4: movement fixes the sensation. So over time, the queue can

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Speaker 4: be as subtle as a tiny joint feeling a moment

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Speaker 4: of stress, or even just seeing your hands, and your

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Speaker 4: brain is cued to add activate that loop.

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Speaker 1: Yes, I know what you're thinking. If knuckle cracking involves

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Speaker 1: the dopamine reward circuit in your brain, does that mean

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Speaker 1: that it's like an addiction. Not quite. According to doctor Godwin,

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Speaker 1: knuckle cracking doesn't quite rise to the level of an addiction,

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Speaker 1: but it can become a compulsion.

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Speaker 4: What distinguishes a habit from a compulsion. As a habit,

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Speaker 4: you identify it, you know it, and you can stop it.

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Speaker 1: Right.

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Speaker 4: It's something that you can interrupt or distract yourself from.

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Speaker 4: The compulsion is a feeling that's almost overwhelming that you

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Speaker 4: must complete the act. It's very much the similar brain circuit,

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Speaker 4: but in the case of compulsive behavior, the dopamine stamp

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Speaker 4: is more profound.

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Speaker 1: I see.

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Speaker 4: But for the most part, there's no reports in the

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Speaker 4: literature that knuckle cracking fits into a category that would

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Speaker 4: identify it as an addiction.

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Speaker 1: I see.

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Speaker 4: There may be somebody out there that has a knuckle

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Speaker 4: cracking addiction. You can't just disclaim that or disprove that,

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Speaker 4: but I would say that it would be pretty rare.

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Speaker 1: You'd call him a real knucklehead.

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Speaker 4: Yeah, or a crackhead. Knuckle crack head.

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Speaker 1: I know, I might get in trouble for them. Now.

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Speaker 1: The good news for knuckle crackers out there is that,

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Speaker 1: as far as anyone knows, popping your joint is not

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Speaker 1: that bad for you. In nineteen ninety eight, a doctor

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Speaker 1: named Donald Unger from Thousand Oaks, California published the letter

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Speaker 1: in the journal Arthritis and Rheumatology, in which he reported

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Speaker 1: the longest running experiment on the subject of knuckle cracking

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Speaker 1: since he was a kid. Doctor Unger had the habit

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Speaker 1: of cracking the knuckles on his left hand, but only

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Speaker 1: on his left hand, not his right hand, and he

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Speaker 1: did it at least twice a day. Fifty years later,

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Speaker 1: in a somewhat tongue in cheek case report in the journal,

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Speaker 1: he was happy to report that after about thirty six

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Speaker 1: five hundred knuckle crackings, neither of his hands head arthritis,

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Speaker 1: and that there was no notice difference in the appearance

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Speaker 1: or health of both hands. For that case report, doctor

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Speaker 1: Hunger was awarded the two thousand and nine ich Noble Prize,

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Speaker 1: which he happily accepted, saying, quote, after about sixty years

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Speaker 1: of knuckle cracking to prove that it does not cause arthritis,

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Speaker 1: perhaps I deserve some sort of award end quote. Now

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Speaker 1: there have been a couple of larger studies. In nineteen

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Speaker 1: ninety a couple of doctors from Mount Carmel Mercy Hospital

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Speaker 1: in Detroit studied a group of three hundred participants, seventy

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Speaker 1: four of which were knuckle crackers. They found that quote,

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Speaker 1: there was no increased preponderance of arthritis of the hand

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Speaker 1: in either group. However, habitual knuckle crackers were more likely

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Speaker 1: to have hand swelling and lower grip strengths. Habitual knuckle

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Speaker 1: cracking was associated with manual labor, biting off the nails, smoking,

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Speaker 1: and drinking alcohol end quote. And In nineteen seventy five,

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Speaker 1: two medical researchers from the University of son Kelvia, Bornia

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Speaker 1: published the study in which they surveyed twenty eight elderly

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Speaker 1: patients about eighty years old and twenty eight kids about

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Speaker 1: eleven years old. They found that just as many kids

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Speaker 1: cracked their knuckles as older people, although they do admit

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Speaker 1: that some of the elderly patients couldn't remember if they

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Speaker 1: cracked their knuckles. But more importantly, they found that the

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Speaker 1: knuckles of the elderly patients who cracked their knuckles weren't

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Speaker 1: just as healthy as the knuckles of the elderly patients

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Speaker 1: who did not crack their knuckles. They concluded, quote, the

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Speaker 1: data fails to support evidence that knuckle cracking leads to

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Speaker 1: degenerative changes in the metacarpal falangeal joints. In old age,

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Speaker 1: the chief morbid consequence of knuckle cracking would appear to

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Speaker 1: be its annoying effect on the observer end quote. Yes,

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Speaker 1: knuckle cracking can be annoying, And it turns out there's

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Speaker 1: actually a name for this. I just have a side question,

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Speaker 1: which is when I hear other people crack your knuckles,

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Speaker 1: it gives me that sense of like, ew oh, what

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Speaker 1: is that.

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Speaker 4: Yeah, there's a condition called misphonia, and it's kin to

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Speaker 4: the fingers on a chalkboard response, yeah, and sort of

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Speaker 4: being grossed out by body horror, that sort of thing.

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Speaker 4: And the idea I think is your brain might interpret

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Speaker 4: the popping of bones and flesh as being something that is,

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Speaker 4: from an evolutionary perspective, something to avoid, uh huh, And

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Speaker 4: so you may be having a response to that.

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Speaker 1: Oh wow, it's tapping into like a very primitive reflex

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Speaker 1: in the brain.

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Speaker 4: Maybe again, you know, there's no literature on this, you know,

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Speaker 4: it's really interesting that what it does point out there's

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Speaker 4: this aspect of the physics of how knuckles pop. There's

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Speaker 4: the sound that comes from it.

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Speaker 1: And that brings us to the last way we will

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Speaker 1: answer the question why do our knuckles cracked, which is

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Speaker 1: by digging into the physics of what's going on. What's

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Speaker 1: actually making that cracking sound? Is it your bones grinding?

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00:23:07,200 --> 00:23:10,760
Speaker 1: Is it something actually popping inside of your joints. When

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Speaker 1: we come back, we'll talk to a Harvard scientist who

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Speaker 1: thinks they finally figured out the real reason our knuckles

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Speaker 1: make that sound, and it's not what you think. So

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Speaker 1: stay with us. We'll be right back. Hey, welcome back.

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Speaker 1: We're cracking the mystery of why we crack our knuckles,

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Speaker 1: and so far we've learned it's related to the kind

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Speaker 1: of joints we have and that it can be a

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Speaker 1: compulsion for some people. Now the question is what actually

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Speaker 1: makes that cracking sound. As it turns out, it's been

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Speaker 1: a mystery in the scientific community for over one hundred years.

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Speaker 1: Here to tell us about it is doctor Vannie Suja,

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Speaker 1: a researcher at the Vis Institute at Harvard University who

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Speaker 1: specializes in bubble physics. Well, thank you, doctor Susjah for

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00:24:18,000 --> 00:24:18,399
Speaker 1: joining us.

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Speaker 3: First, my pleasure and it's great to see you.

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Speaker 1: Okay, my first question is do you crack your knuckles.

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Speaker 3: Oh, I do. And one of these people who has

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Speaker 3: this compulsive disorder, you know, I cracked my knuckles whenever

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Speaker 3: we're I'm frustrated when something doesn't work, and that's more

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Speaker 3: days in my life than usual.

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Speaker 4: Right.

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Speaker 1: Can we hear your knuckles cracking right now?

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Speaker 3: Yeah? Let me try.

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Speaker 1: Did you hear some Yeah that was pretty fun. Yeah,

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Speaker 1: that's really dense. Now. In twenty eighteen, doctor Suja was

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Speaker 1: the lead author of the paper titled A Mathematical Model

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Speaker 1: of the Sounds Produced by Knuckle Cracking, in which they

435
00:24:56,560 --> 00:24:59,720
Speaker 1: claim to finally settle the debate of what actually makes

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00:24:59,760 --> 00:25:03,280
Speaker 1: the that happens when we crack our knuckles. It's a

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00:25:03,359 --> 00:25:06,159
Speaker 1: debate that, according to doctor Suja, has been going on

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Speaker 1: for over one hundred years. Tell us the history of

439
00:25:10,840 --> 00:25:12,960
Speaker 1: trying to figure out where the sound comes from.

440
00:25:13,320 --> 00:25:15,359
Speaker 3: Yeah, we were able to trace it back to at

441
00:25:15,440 --> 00:25:19,200
Speaker 3: least the early nineteen hundreds, where there's actual published scientific

442
00:25:19,280 --> 00:25:23,400
Speaker 3: literature on people saying, look, not everybody can crack their knuckles,

443
00:25:24,160 --> 00:25:26,000
Speaker 3: so people kind of like document their way back.

444
00:25:26,840 --> 00:25:30,399
Speaker 1: According to doctor Suja, one breakthrough came in nineteen forty

445
00:25:30,480 --> 00:25:34,359
Speaker 1: seven to doctors from the Saint Thomas Hospital Medical School

446
00:25:34,440 --> 00:25:38,560
Speaker 1: in London decided to do experiments on actual fingers, measuring

447
00:25:38,720 --> 00:25:41,280
Speaker 1: how much tension was needed and how far apart the

448
00:25:41,400 --> 00:25:45,080
Speaker 1: joints needed to be to create a crack, and they

449
00:25:45,160 --> 00:25:47,400
Speaker 1: realized that it might have something to do with how

450
00:25:47,680 --> 00:25:49,560
Speaker 1: sudden the joint snaps.

451
00:25:51,000 --> 00:25:53,480
Speaker 3: They said, like, it has to do with how quickly

452
00:25:53,600 --> 00:25:56,600
Speaker 3: the joints are being separated. There's something there and they

453
00:25:56,760 --> 00:25:59,600
Speaker 3: kind of concluded that when you do this so fast,

454
00:25:59,680 --> 00:26:01,520
Speaker 3: you know, could be vibrations and a tissue and that

455
00:26:01,640 --> 00:26:02,440
Speaker 3: could be the sound.

456
00:26:03,440 --> 00:26:06,359
Speaker 1: But then in nineteen seventy one, another group of British

457
00:26:06,400 --> 00:26:09,280
Speaker 1: scientists for the University of Leads decided to make a

458
00:26:09,440 --> 00:26:12,520
Speaker 1: plastic model of a joint, put some fluid in it,

459
00:26:12,840 --> 00:26:15,240
Speaker 1: and they use the high speed camera to see what

460
00:26:15,400 --> 00:26:17,320
Speaker 1: happens when you pop the joint.

461
00:26:18,280 --> 00:26:21,280
Speaker 3: They actually build a kind of mockup model of the

462
00:26:21,359 --> 00:26:26,320
Speaker 3: tissue and they could see some bubble activity happening as

463
00:26:26,400 --> 00:26:30,200
Speaker 3: they were pulling about this joint and they said it's cavitation.

464
00:26:31,240 --> 00:26:33,720
Speaker 1: And here we get to what scientists think is the

465
00:26:33,880 --> 00:26:39,200
Speaker 1: culprit makes the knuckle cracking sound. Cavitation. Cavitation is what

466
00:26:39,320 --> 00:26:44,919
Speaker 1: happens when you suddenly get bubbles inside of a liquid. Now,

467
00:26:45,119 --> 00:26:47,440
Speaker 1: one way to get bubbles inside a liquid is to

468
00:26:47,760 --> 00:26:50,480
Speaker 1: boil it. When you heat water on a stove, the

469
00:26:50,600 --> 00:26:53,480
Speaker 1: water molecules at the bottom get hot and they turn

470
00:26:53,600 --> 00:26:56,880
Speaker 1: to steam, which is a gas, and so they form bubbles.

471
00:26:57,320 --> 00:26:59,720
Speaker 1: But another way to turn water to gas is to

472
00:27:00,080 --> 00:27:02,880
Speaker 1: lower the pressure. If you put a glass of water

473
00:27:03,040 --> 00:27:06,119
Speaker 1: in a vacuum chamber, you'll start to bubble and boil,

474
00:27:06,440 --> 00:27:09,240
Speaker 1: even if it's a room temperature. It's sort of like

475
00:27:09,280 --> 00:27:11,479
Speaker 1: when you open a can of soda.

476
00:27:13,520 --> 00:27:15,840
Speaker 3: The best anology I can draw is like opening a

477
00:27:15,880 --> 00:27:19,400
Speaker 3: soda bottle. It's pressureized, right, and like you open the cap,

478
00:27:19,800 --> 00:27:23,359
Speaker 3: you're suddenly changing the pressure. And what that leads to

479
00:27:23,800 --> 00:27:25,760
Speaker 3: is sort of bubbles coming out.

480
00:27:26,080 --> 00:27:28,640
Speaker 1: And so here's what those scientists in nineteen seventy one

481
00:27:28,960 --> 00:27:32,439
Speaker 1: thought was happening. When you're cracking your knuckles, you're bending

482
00:27:32,520 --> 00:27:35,440
Speaker 1: your joints, but at some point you can over bend

483
00:27:35,520 --> 00:27:38,920
Speaker 1: them and that pulls the two bones apart. But there's

484
00:27:38,960 --> 00:27:42,320
Speaker 1: fluid in between them, and so that fluid gets stretched,

485
00:27:42,520 --> 00:27:47,639
Speaker 1: which causes the pressure to drop and you form bubbles. Now,

486
00:27:47,760 --> 00:27:50,520
Speaker 1: the scientists in nineteen seventy one saw the bubbles in

487
00:27:50,560 --> 00:27:54,040
Speaker 1: their model and they thought, ah, that's what's making the

488
00:27:54,160 --> 00:27:57,879
Speaker 1: cracking sound. It's the bubbles from cavitation popping.

489
00:28:00,119 --> 00:28:02,840
Speaker 3: This is sort of like the rapid formation and collapse

490
00:28:02,880 --> 00:28:06,320
Speaker 3: of bubbles that had been known to like damage propellers

491
00:28:06,400 --> 00:28:09,639
Speaker 3: with these bubbles, and that ended up being like the

492
00:28:09,760 --> 00:28:11,680
Speaker 3: state of the art for a long time. And remember

493
00:28:11,760 --> 00:28:14,240
Speaker 3: growing up and like it whenever somebody asked me what

494
00:28:14,400 --> 00:28:17,560
Speaker 3: causes the sound of it's a gavitation, because that used

495
00:28:17,600 --> 00:28:18,200
Speaker 3: to be the thing.

496
00:28:19,600 --> 00:28:22,320
Speaker 1: As doctor Suji said, this is what people thought caused

497
00:28:22,359 --> 00:28:25,840
Speaker 1: knuckle cracking for a long time. It's the bubbles from

498
00:28:25,920 --> 00:28:30,359
Speaker 1: cavitation in the joint popping, right, that makes sense. But

499
00:28:30,480 --> 00:28:34,080
Speaker 1: then about forty years later, in twenty fifteen, a group

500
00:28:34,119 --> 00:28:37,919
Speaker 1: of Canadian and Australian engineers and doctors decided to get

501
00:28:38,000 --> 00:28:41,160
Speaker 1: more high tech and they used an MRI machine to

502
00:28:41,240 --> 00:28:44,640
Speaker 1: see what was going on inside of an actual knuckle.

503
00:28:46,000 --> 00:28:49,840
Speaker 3: They actually did the first imaging study. They used MRI

504
00:28:50,840 --> 00:28:54,440
Speaker 3: to look inside the knuckles and as we said before,

505
00:28:55,000 --> 00:28:58,840
Speaker 3: MRA is slow, definitely cannot see what's happening at the

506
00:28:58,920 --> 00:29:02,320
Speaker 3: moment these sounds are coming. But what they could see

507
00:29:02,520 --> 00:29:06,360
Speaker 3: was at slow enough time points, they could actually see

508
00:29:06,400 --> 00:29:09,440
Speaker 3: the bubble there, oh, and it persisted.

509
00:29:10,600 --> 00:29:14,080
Speaker 1: What the Canadian engineers and doctors saw was that even

510
00:29:14,200 --> 00:29:17,239
Speaker 1: after the knuckle had made the cracking sound, there were

511
00:29:17,360 --> 00:29:21,680
Speaker 1: still bubbles. The bubbles hadn't popped. But if the bubbles

512
00:29:21,720 --> 00:29:24,040
Speaker 1: hadn't popped, what made the cracking sound?

513
00:29:26,280 --> 00:29:30,120
Speaker 3: And that gave them an interesting idea. So they said, look,

514
00:29:30,160 --> 00:29:34,000
Speaker 3: there's bubbles still in there. Maybe it's not a collapse,

515
00:29:34,280 --> 00:29:37,200
Speaker 3: but it is a formation of these bubbles that could

516
00:29:37,240 --> 00:29:41,959
Speaker 3: be the source of the sound. So that suddenly opened up,

517
00:29:42,160 --> 00:29:44,360
Speaker 3: you know, more questions, and the flood gates of questions,

518
00:29:44,400 --> 00:29:47,160
Speaker 3: and suddenly, like the knuckle cracking was in the debdfield again.

519
00:29:48,320 --> 00:29:52,800
Speaker 1: Yes, the entire knuckle cracking research field was thrown into

520
00:29:53,120 --> 00:29:56,280
Speaker 1: this array. Okay, to be honest, there aren't that many

521
00:29:56,320 --> 00:29:58,680
Speaker 1: people looking into this. I mean, it's not like the

522
00:29:58,760 --> 00:30:02,040
Speaker 1: government and foundations are pouring billions of dollars to figure

523
00:30:02,040 --> 00:30:05,120
Speaker 1: out knuckle cracking. But still it became a topic of

524
00:30:05,320 --> 00:30:09,160
Speaker 1: debate again. Was knuckle cracking caused by bubbles forming in

525
00:30:09,200 --> 00:30:12,240
Speaker 1: the liquid inside the knuckle joints or was it caused

526
00:30:12,280 --> 00:30:16,760
Speaker 1: by the bubbles popping. That's when doctor Sujah entered the picture.

527
00:30:18,440 --> 00:30:21,040
Speaker 3: So this is more than a decade back. And I

528
00:30:21,280 --> 00:30:23,200
Speaker 3: was in Frans as a master's student.

529
00:30:23,640 --> 00:30:23,840
Speaker 2: You know.

530
00:30:23,960 --> 00:30:26,400
Speaker 3: I was in this class of a wonderful professor by

531
00:30:26,440 --> 00:30:28,760
Speaker 3: the name of Abdel Barka, and he said, I have

532
00:30:28,840 --> 00:30:31,600
Speaker 3: two weeks to figure out an interesting problem in buying mechanics,

533
00:30:31,680 --> 00:30:35,719
Speaker 3: and sought okay. And I'm like sitting in frustration, kind

534
00:30:35,720 --> 00:30:39,400
Speaker 3: of cracking my knuckles, and Sally like, oh, this seems

535
00:30:39,400 --> 00:30:42,040
Speaker 3: to be an interesting problem. You knows buying mechanics in

536
00:30:42,120 --> 00:30:44,719
Speaker 3: there and read more about it, and there's flood mechanics

537
00:30:44,760 --> 00:30:47,280
Speaker 3: in there, there's bubble physics, and I got all excited.

538
00:30:48,840 --> 00:30:52,840
Speaker 1: What doctor Suja did was create the most accurate mathematical

539
00:30:52,960 --> 00:30:56,320
Speaker 1: model of the physics of joint bubble formation that had

540
00:30:56,480 --> 00:31:00,880
Speaker 1: ever been done. Okay, let me through what you did.

541
00:31:01,000 --> 00:31:03,320
Speaker 1: So in a computer you wrote up a simulation of

542
00:31:03,440 --> 00:31:04,440
Speaker 1: what we ended.

543
00:31:04,360 --> 00:31:08,800
Speaker 3: Up modeling three critical events mathematically. So one is how

544
00:31:08,880 --> 00:31:12,080
Speaker 3: the pressure is changing, and there's a so called lubrication

545
00:31:12,280 --> 00:31:15,040
Speaker 3: theory that's in fluid mechanics we can leverage to predict

546
00:31:15,160 --> 00:31:18,640
Speaker 3: how fluid pressure changes when there's motion in a small

547
00:31:18,760 --> 00:31:22,240
Speaker 3: enough gap, so we use that. And second, there's a

548
00:31:22,480 --> 00:31:26,000
Speaker 3: really intriguing theory that basically describes what happens to a

549
00:31:26,040 --> 00:31:29,480
Speaker 3: bubble in the fluid where the pressure is changing. So

550
00:31:29,600 --> 00:31:32,560
Speaker 3: we know how the pressure change is quantitatively, we know

551
00:31:32,680 --> 00:31:34,680
Speaker 3: how this bubble is going to respond to that pressure,

552
00:31:35,240 --> 00:31:38,480
Speaker 3: and finally we wander to link this pressure to the

553
00:31:38,600 --> 00:31:41,160
Speaker 3: sound we hear. So there's another set of equations that

554
00:31:41,360 --> 00:31:46,200
Speaker 3: go from this pressure oscillations to audible sound. So three equations.

555
00:31:47,160 --> 00:31:50,080
Speaker 1: Okay, the details here get a little technical. It turns

556
00:31:50,120 --> 00:31:53,080
Speaker 1: out that there are several ways that the cavitation bubbles

557
00:31:53,120 --> 00:31:55,520
Speaker 1: in the joint can be made, either from the liquid

558
00:31:55,600 --> 00:31:59,040
Speaker 1: being pulled apart or the liquid being stretched by friction.

559
00:31:59,520 --> 00:32:02,600
Speaker 1: And there's also what happens after the joint gets pulled apart,

560
00:32:02,760 --> 00:32:05,440
Speaker 1: which is that the pressure goes up again because flood

561
00:32:05,560 --> 00:32:07,840
Speaker 1: rushes in to fill the gap. But the point is

562
00:32:07,920 --> 00:32:10,920
Speaker 1: that doctor Suja modeled all of this and he simulated

563
00:32:10,960 --> 00:32:13,920
Speaker 1: the sound the bubbles would make, and then he compared

564
00:32:13,960 --> 00:32:17,480
Speaker 1: it to the sound of actual people cracking their knuckles.

565
00:32:19,160 --> 00:32:22,640
Speaker 1: And then you tested this by bringing people into an

566
00:32:22,720 --> 00:32:26,880
Speaker 1: antichoic chamber and having them crack their knuckles. Yes, how

567
00:32:26,920 --> 00:32:28,840
Speaker 1: did you find people who could crack their knuckles?

568
00:32:29,080 --> 00:32:31,640
Speaker 3: A lot of people who love cracking knuckles and like

569
00:32:31,800 --> 00:32:34,240
Speaker 3: helping out for the name of science. So you know,

570
00:32:34,280 --> 00:32:36,720
Speaker 3: it was at the university, and there's a lot of

571
00:32:36,760 --> 00:32:42,680
Speaker 3: frustrated pieces. Yes, we did briefly advertise this study, but

572
00:32:43,080 --> 00:32:46,240
Speaker 3: you know, mostly what of mouth as he put a

573
00:32:46,320 --> 00:32:48,000
Speaker 3: microphone right next to somebody's knuckle.

574
00:32:48,200 --> 00:32:49,080
Speaker 1: Yeah, that's precisely.

575
00:32:49,120 --> 00:32:51,480
Speaker 3: What of those like we had people set in like

576
00:32:51,600 --> 00:32:54,640
Speaker 3: a recording studio and have people come in and crack

577
00:32:54,680 --> 00:32:56,320
Speaker 3: the knuckles close to a microphone.

578
00:32:56,400 --> 00:32:58,360
Speaker 1: Did you have them work on their thesis so that

579
00:32:58,400 --> 00:32:59,360
Speaker 1: they would get frustrated?

580
00:33:00,720 --> 00:33:01,880
Speaker 3: That wou'd have been a good point. I know we

581
00:33:01,960 --> 00:33:03,600
Speaker 3: could have gotten more volunteers that way.

582
00:33:05,160 --> 00:33:09,040
Speaker 1: So doctor Suja compared the frequency signature the sound from

583
00:33:09,120 --> 00:33:13,680
Speaker 1: his mathematical simulation to the signature of real knuckle cracks,

584
00:33:14,080 --> 00:33:18,560
Speaker 1: and they matched. But here's the thing. In doctor Suji's simulation,

585
00:33:19,000 --> 00:33:23,040
Speaker 1: the sound didn't come from either the bubbles forming or

586
00:33:23,560 --> 00:33:24,680
Speaker 1: the bubbles popping.

587
00:33:26,280 --> 00:33:29,880
Speaker 3: And what our modeling work showed was you could still

588
00:33:30,120 --> 00:33:34,840
Speaker 3: have a collapsing bubble and produce sounds, but the bubble

589
00:33:34,960 --> 00:33:38,680
Speaker 3: need not collapse completely for the sounds to happen. You

590
00:33:38,760 --> 00:33:41,640
Speaker 3: don't need the bubble to go to a size of zero,

591
00:33:42,000 --> 00:33:44,560
Speaker 3: but it could be like starting with something big, going

592
00:33:44,600 --> 00:33:47,920
Speaker 3: to ten times smaller and stop there. And still that

593
00:33:48,160 --> 00:33:53,800
Speaker 3: partial change in size was sufficient to explain the sounds. Okay, okay,

594
00:33:53,920 --> 00:33:56,600
Speaker 3: so you can still see the bubble after knuckle cracking.

595
00:33:57,400 --> 00:34:00,760
Speaker 1: What doctor Suji's model showed was that the popping sound

596
00:34:01,080 --> 00:34:05,120
Speaker 1: actually comes from the bubbles shrinking, not when they form,

597
00:34:05,640 --> 00:34:09,120
Speaker 1: not when they pop, when the bubbles shrink, And that

598
00:34:09,239 --> 00:34:12,680
Speaker 1: seems to be the best explanation we have about where

599
00:34:12,760 --> 00:34:17,920
Speaker 1: the knuckle cracking sound comes from. All right, and say,

600
00:34:18,080 --> 00:34:21,720
Speaker 1: you've helped partially resolve this big mystery that's been sitting

601
00:34:21,760 --> 00:34:23,319
Speaker 1: around for over fifty years.

602
00:34:23,520 --> 00:34:23,960
Speaker 3: Partially.

603
00:34:24,040 --> 00:34:24,239
Speaker 1: Yeah.

604
00:34:24,440 --> 00:34:26,680
Speaker 3: The cool thing is we were able to like kind

605
00:34:26,680 --> 00:34:28,600
Speaker 3: of say, maybe both of you guys can be right

606
00:34:28,640 --> 00:34:30,640
Speaker 3: the nineteen seventy one and twenty fifteen, and there's a

607
00:34:30,719 --> 00:34:31,879
Speaker 3: way to go forward from there.

608
00:34:32,560 --> 00:34:36,319
Speaker 1: And as a bonus, doctor Sugis's model actually predicts why

609
00:34:36,440 --> 00:34:39,840
Speaker 1: some people can crack their knuckles and some people can't.

610
00:34:40,320 --> 00:34:42,960
Speaker 3: And a good thing about mathematical moral and a lot

611
00:34:43,000 --> 00:34:47,120
Speaker 3: of marveling for this reasons. You can quantitatively say how

612
00:34:47,600 --> 00:34:50,920
Speaker 3: certain parameters and this problem in fact the sound. For example,

613
00:34:50,960 --> 00:34:53,400
Speaker 3: what if you have a different joint spacing. What if

614
00:34:53,440 --> 00:34:55,280
Speaker 3: you pull the join a little bit harder?

615
00:34:55,880 --> 00:34:56,040
Speaker 2: Right?

616
00:34:56,239 --> 00:34:58,839
Speaker 3: And why can't some people crack their knuckles? The model

617
00:34:58,880 --> 00:35:02,279
Speaker 3: says they are the only spacing is too large. You

618
00:35:02,360 --> 00:35:06,959
Speaker 3: won't be able to generate precious low enough to cause

619
00:35:07,080 --> 00:35:09,120
Speaker 3: the bubbles to form an oslate in a way that

620
00:35:09,200 --> 00:35:10,000
Speaker 3: can produce.

621
00:35:09,719 --> 00:35:13,640
Speaker 1: The sound amazing? Has this changed how you see your

622
00:35:13,719 --> 00:35:15,719
Speaker 1: knuckles or when you crack your nuckles? Do you think

623
00:35:15,760 --> 00:35:16,719
Speaker 1: about it differently now?

624
00:35:17,000 --> 00:35:17,160
Speaker 3: Yes?

625
00:35:17,280 --> 00:35:17,480
Speaker 4: And no.

626
00:35:17,960 --> 00:35:20,040
Speaker 1: Could you go back to your mother and say, see, mom,

627
00:35:20,160 --> 00:35:23,640
Speaker 1: every time I cracked my knuckles, that was good for something? Yeah?

628
00:35:23,840 --> 00:35:25,600
Speaker 3: And the response I would get is like, do you

629
00:35:25,680 --> 00:35:28,800
Speaker 3: have no other, you know, important scientific problem to think about?

630
00:35:32,400 --> 00:35:35,239
Speaker 1: It's never enough, is it right? Exactly? Yeah? It's like,

631
00:35:35,280 --> 00:35:37,040
Speaker 1: why aren't you curring cancer? Why are you trying to

632
00:35:37,080 --> 00:35:38,160
Speaker 1: figure out knuckle cracking?

633
00:35:38,600 --> 00:35:40,640
Speaker 3: Do you have too much time on your plate?

634
00:35:40,800 --> 00:35:43,600
Speaker 1: Stop cracking your knuckles and get to work on something important.

635
00:35:43,920 --> 00:35:44,160
Speaker 2: Yeah?

636
00:35:45,480 --> 00:35:49,360
Speaker 1: All right. Well to recap as annoying as someone cracking

637
00:35:49,400 --> 00:35:52,880
Speaker 1: their knuckles is, it's all because we have these fluid

638
00:35:52,960 --> 00:35:57,120
Speaker 1: filled joints. Let us do amazing movements like walking and

639
00:35:57,280 --> 00:36:02,120
Speaker 1: running and climbing. It's not issarily harmful to crack your knuckles,

640
00:36:02,520 --> 00:36:05,759
Speaker 1: even if you do it compulsively, and hey, it could

641
00:36:05,880 --> 00:36:08,680
Speaker 1: end up getting you a PhD and a job at Harvard.

642
00:36:09,080 --> 00:36:12,839
Speaker 1: You just have to knuckle down. Thanks for joining us,

643
00:36:13,480 --> 00:36:17,360
Speaker 1: see you next time. Hey, a big shout out to

644
00:36:17,480 --> 00:36:20,800
Speaker 1: doctor Gage Crump. We also interviewed about the evolution of

645
00:36:20,800 --> 00:36:24,840
Speaker 1: sinolial joints and to our editor Rose, who can't stand

646
00:36:25,239 --> 00:36:28,240
Speaker 1: people cracking their knuckles, so the fact that she edited

647
00:36:28,280 --> 00:36:32,399
Speaker 1: this episode is a huge active bravery and commitment. Thanks

648
00:36:32,400 --> 00:36:37,960
Speaker 1: to Rose. Oh and also, this week is Brain Awareness Week,

649
00:36:38,200 --> 00:36:40,319
Speaker 1: so if you're interested in learning more about the brain,

650
00:36:40,719 --> 00:36:43,480
Speaker 1: check out my book with doctor Dwayne Godwin, Out of

651
00:36:43,600 --> 00:36:50,360
Speaker 1: Your Mind, available wherever books are sold. You've been listening

652
00:36:50,400 --> 00:36:54,720
Speaker 1: to Science Stuff the production of iHeartRadio, written and produced

653
00:36:54,719 --> 00:36:58,719
Speaker 1: by me or Y Champ, candited by Rose Seguda, executive

654
00:36:58,719 --> 00:37:02,759
Speaker 1: producer Jerry Rowland, audio engineer and mixer Ksey Pegram, and

655
00:37:02,840 --> 00:37:05,000
Speaker 1: you can follow me on social media. Just search for

656
00:37:05,200 --> 00:37:08,279
Speaker 1: PhD Comics and the name of your favorite platform. Be

657
00:37:08,400 --> 00:37:11,120
Speaker 1: sure to subscribe to Sign Stuff on the iHeartRadio app,

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00:37:11,239 --> 00:37:14,400
Speaker 1: Apple Podcasts or wherever you get your podcasts, and please

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00:37:14,640 --> 00:37:27,120
Speaker 1: tell your friends we'll be back next Wednesday with another episode. Hey,

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00:37:27,440 --> 00:37:29,279
Speaker 1: please take a second and leave us a review on

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00:37:29,480 --> 00:37:33,000
Speaker 1: Apple Podcasts, Spotify, or wherever you listen to the podcast.

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00:37:33,719 --> 00:37:34,200
Speaker 1: Thanks a lot,