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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.
Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
Human kidneys will clean about 1 million gallons of blood in an average lifetime.
Cyanide works by making the human body unable to use oxygen.