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There are 20 feet of blood vessels in each square inch of human skin.
Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
Stroke kills people from all ethnic backgrounds, but the people at highest risk for fatal strokes are: black men, black women, Asian men, white men, and white women.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.