Prank stink bombs and perfume bombs are usually sold as a 1- or 2-mL sealed glass ampoule, which can be broken by throwing against a hard surface or by crushing under one's shoe sole, thus releasing the malodorous liquid contained therein. Another variety of prank stink bomb comprises two bags, one smaller and inside the other. The inner one contains a liquid and the outer one a powder. When the inner one is ruptured by squeezing it, the liquid reacts with the powder, producing hydrogen sulfide, which expands and bursts the outer bag, releasing an unpleasant odor.