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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.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Approximately 70% of expectant mothers report experiencing some symptoms of morning sickness during the first trimester of pregnancy.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.