Re: How can a gum wrapper produce heat?

What a great trick! I did a quick Google search and found the following explanation at science.ca for what you saw:

There's an old "Bar bet" wherein the person takes the Aluminum foil from a cigarette pack, wets is with some Hg2Cl2 and pinches it between both thumbs and forefingers, and says "I bet you can't hold in your hand what I've got in mine." The sucker accepts the "gift" of reactive Al foil and gets a burn as the air oxidation causes it to heat up. The Bichloride of Mercury used to be available as an antiseptic.
The chloride ion will break down the oxide layer on the aluminum, allowing the aluminum to oxidize assuming there's some water present to ionize the mercurous chloride.

Note: Mercury bichloride is poisonous if swallowed. Please read the Materia l Safety Data Sheets for more information about this compound. Remember, magic is fun but also should be safe. :)

Kieran