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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
Though the United States has largely rejected the metric system, it is used for currency, as in 100 pennies = 1 dollar. Previously, the British currency system was used, with measurements such as 12 pence to the shilling, and 20 shillings to the pound.
About 600,000 particles of skin are shed every hour by each human. If you live to age 70 years, you have shed 105 pounds of dead skin.
The eye muscles are the most active muscles in the whole body. The external muscles that move the eyes are the strongest muscles in the human body for the job they have to do. They are 100 times more powerful than they need to be.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."