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The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Earwax has antimicrobial properties that reduce the viability of bacteria and fungus in the human ear.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
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.