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Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
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.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.