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Speaker 1: Welcome to brain stuff from how stuff works. Hey, brain stuff,

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Speaker 1: it's Christian saga. Do you remember in the movie Carry

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Speaker 1: where they dumped pig blood on that girl at her prom? Well?

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Speaker 1: The Annals of Human Biology actually published an article in

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Speaker 1: two thousand twelve showing that humans are excellent detectors of

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Speaker 1: pig blood, but we are far less developed at detecting

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Speaker 1: human blood. They concluded that human blood has no specific

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Speaker 1: smell or appearance that triggers immediate recognition. So blood is

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Speaker 1: always red, right, But why does it have to be read?

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Speaker 1: Contrary to popular belief, it's not blue when it's in

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Speaker 1: our bodies, even when it's deoxygenated. But oxygen is part

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Speaker 1: of the color, along with the protein molecule hemoglobin that

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Speaker 1: attaches to oxygen. It carries from the lungs two muscles

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Speaker 1: as blood gets pumped through the human body. And while

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Speaker 1: blood is always red, its shade depends on how much

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Speaker 1: oxygen it's carrying. For instance, when you cut a person's

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Speaker 1: arteries open, they bleed this really bright red blood because

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Speaker 1: of the complex formed between hemoglobin, iron and lots of oxygen.

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Speaker 1: But if you look deeper into the circulatory system and

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Speaker 1: peered into a vein that was delivering all of its oxygen,

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Speaker 1: you would see that the blood is a deeper maroon color,

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Speaker 1: So veins they look blue or green mainly because of

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Speaker 1: skin and skin pigmentation plays a big role. Since everyone's

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Speaker 1: skin is a different color, our veins look different, especially

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Speaker 1: because the tissue above our veins scatters red light, but

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Speaker 1: let's blue light right on through. Even though veins are

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Speaker 1: a reddish brown, they appear to be blue from the outside.

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Speaker 1: So is the way human beings perceive color and other

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Speaker 1: factor here as well. Yes, researchers have shown that it

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Speaker 1: is partially an optical illusion. So light colored skin reflects

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Speaker 1: most light and blood absorbs most light, particularly dark deoxygenated blood.

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Speaker 1: It reflects a little blue and some red, But since

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Speaker 1: the skin surrounding the veins scatters and reflects a lot

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Speaker 1: of red light, the veins look way bluer in comparison.

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Speaker 1: The ratio is so skewed that it tricks the eye.

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Speaker 1: In fact, some animals actually bleed other colors, like slugs

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Speaker 1: and molluscs, they bleed blue. Check out the brain stuff

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Speaker 1: channel on YouTube, and for more on this and thousands

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Speaker 1: of other topics, visit how stuff works dot com,