system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the science behind TNT Pop-Its (Snap Bags)? What makes them explode when you throw them at something?

My company bought a really old ice cream truck to refurbish, and we found a goldmine of old candy and toys inside.  Amongst all the crap was a box of TNT Pop-Its. We've been scaring each other by throwing them around the office all week, and it's been making me wonder about how exactly they work.
gpt
Inside the tiny bag is ~99.99% gravel or sand, the other 0.01% is a chemical called silver fulminate. It's a highly unstable chemical that ignites under any sort of friction ( by dropping, squeezing, or stepping on it). When the chemical ignites it creates a shockwave that travels faster than the speed of sound and that's where the "snap" sound comes from (kind of like how a whip makes its noise). This shockwave is extremely weak and that's why you can pop one in your hand and it wont hurt.