Subject: How can a gum wrapper produce heat?

About 10 years ago, I knew a woman that did a "magic trick" that she said she 
saw at a science convention. She would have herself or someone else soak a gum 
wrapper(always foil and seemed to not matter what flavor) in saliva. She would 
then take the foil, smooth it out, and fold(silver side out)it in half until 
you couldn't fold it any more. Then you lay it in the palm of someone's hand 
and seconds later it becomes so hot it becomes impossible to hold without 
burning yourself. I had asked her to do one on the spot once with my own gum 
foil, and she said give me a couple of minutes. She was able to do it after 
obviously retrieving an addition to the trick. She refuses to tell the secret. 
I have asked several professors and researched myself, but can not find out 
what it is that she is adding to the equation to create such a great amount of 
heat. Please help.

Re: How can a gum wrapper produce heat?