This is probably one of the weirdest questions on here. When I was a kid, I put aluminum foil in my mouth (maybe it was still attached to some food or something, I don't remember.)
Anyway, it made my mouth feel like I'd licked a 9-volt battery. Being the natural born scientist, I repeated the procedure with similar results.
Why does this happen? I really think it has something to do with my dental fillings since the sensation occurred near them.