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Did you know?
The familiar sounds of your heart are made by the heart's valves as they open and close.
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The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
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Your heart beats over 36 million times a year.
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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.
Did you know?
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.