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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.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Bacteria have been found alive in a lake buried one half mile under ice in Antarctica.
When Gabriel Fahrenheit invented the first mercury thermometer, he called "zero degrees" the lowest temperature he was able to attain with a mixture of ice and salt. For the upper point of his scale, he used 96°, which he measured as normal human body temperature (we know it to be 98.6° today because of more accurate thermometers).
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.