Bang snaps (sometimes called party poppers, risking confusion with a different party pyrotechnic that goes by this name) are a type of small firework that can be thrown to trigger a minor explosion upon impact. They are so small that this explosion is basically harmless; it causes no injury even if discharged in the hand, producing only noise. The “crack” sound comes from a supersonic shockwave which is generated by the explosion of a very small amount of silver fulminate, triggered via friction.
