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There are more bacteria in your mouth than there are people in the world.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
There are more nerve cells in one human brain than there are stars in the Milky Way.
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.
Patients who cannot swallow may receive nutrition via a parenteral route—usually, a catheter is inserted through the chest into a large vein going into the heart.