WHOA!
That's what the students always say when a drop of human spit activates a mixture of 1gram NH₄Cl, 4grams NH₄NO₃, and 4grams Zn.

CHEMICAL NAMES

NH4Cl=Ammonium Chloride

NH4NO3=Ammonium Nitrate

Zn=Zinc

Here's the deal (as I understand it, anyway)... Zn has a couple spare electrons that it's not holding too tightly.  The NH₄NO₃ has atoms that want more electrons.  The drop of spit provides the energy necessary to start the reaction.  Here's a picture of the reaction in our fume hood.  (Sorry about the flash showing up in the glass!)
Small beaker, big fire!