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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 horizontal fraction bar was introduced by the Arabs.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
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.
Of the estimated 2 million heroin users in the United States, 600,000–800,000 are considered hardcore addicts. Heroin addiction is considered to be one of the hardest addictions to recover from.