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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.
On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.
Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.