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Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
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).
Oliver Wendell Holmes is credited with introducing the words "anesthesia" and "anesthetic" into the English language in 1846.
It is difficult to obtain enough calcium without consuming milk or other dairy foods.