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The familiar sounds of your heart are made by the heart's valves as they open and close.
Drying your hands with a paper towel will reduce the bacterial count on your hands by 45–60%.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.