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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.
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.
Pregnant women usually experience a heightened sense of smell beginning late in the first trimester. Some experts call this the body's way of protecting a pregnant woman from foods that are unsafe for the fetus.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.