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The familiar sounds of your heart are made by the heart's valves as they open and close.
According to the American College of Allergy, Asthma & Immunology, more than 50 million Americans have some kind of food allergy. Food allergies affect between 4 and 6% of children, and 4% of adults, according to the CDC. The most common food allergies include shellfish, peanuts, walnuts, fish, eggs, milk, and soy.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
The word drug comes from the Dutch word droog (meaning "dry"). For centuries, most drugs came from dried plants, hence the name.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.