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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
The most dangerous mercury compound, dimethyl mercury, is so toxic that even a few microliters spilled on the skin can cause death. Mercury has been shown to accumulate in higher amounts in the following types of fish than other types: swordfish, shark, mackerel, tilefish, crab, and tuna.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
If you could remove all of your skin, it would weigh up to 5 pounds.