Biting on aluminum foil can be painful because it creates a voltaic battery in your mouth. This happens when the foil comes into contact with metal from dental work in a moist, saline environment like saliva. This contact generates an electrical current that flows to the tooth’s root, stimulating nerve endings and causing pain, especially if you have fillings, crowns or other metal dental work.
I might eat some paper because it was on there and you don’t really taste it, but if I touched my teeth to tin foil, I would instantly feel it.
It’s like it completes a circuit or something. That shit hurts.
And I have fillings, too. IDK if you know how much more that affects it, but it’s like being zapped directly in your brain.
Not your brain, the root of your tooth:
https://science.howstuffworks.com/question564.htm