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The average adult has about 21 square feet of skin.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
If you could remove all of your skin, it would weigh up to 5 pounds.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
There are 60,000 miles of blood vessels in every adult human.
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