I Didn’t Know That ...

Q: Why is biting on aluminum foil painful?

A: Biting on the foil is painful only to people with mercury fillings or gold crowns because it produces a battery, which sends an electrical shock through nerves in the teeth. Batteries are produced by combining two dissimilar metals in a moist, salty environment. In this case, the metals are aluminum and either mercury or gold, and your saliva provides the appropriate environment. The phenomenon is called the voltaic effect, after Alessandro Volta, who stacked metal discs together to make the first crude batteries.