agencies and militaries as riot control and area denial weapons. Using stink bombs for these purposes has advantages over traditional riot control agents: unlike pepper spray and tear gas, stink bombs are believed not to be dangerous, although their psychological effects can make people sick. 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. Chemicals used Typically, lower molecular weight volatile organic compounds are used. Generally the higher molecular weight for a given class of compounds, the lower volatility and initial concentration but the longer persistence. Some chemicals (typically thiols) have a certain concentration threshold over which the smell is not perceived significantly stronger; therefore a lower-volatility compound is capable of providing comparable stench intensity to a higher-volatility compound, but for longer time. Another issue is the operating temperature, on which the compound's volatility strongly depends. Care should be taken as some compounds are toxic either in higher concentration or after prolonged exposure in low concentration. Some plants may be used as improvised stink bombs; one such plant is the Parkia speciosa or 'stinky bean', which grows in India, Southeast Asia and Eastern Australia. The pods from this plant are collected when partly dried and stamped on, to release the stink. Some common components are: Organosulfur compounds Methanethiol (used rarely; it is a gas and therefore more difficult to handle than liquids) Ethanethiol, smelling similar to leeks, onions, durian or cooked cabbage Propanethiol Butanethiol, smelling similar to skunk spray Inorganic sulfur compounds Ammonium sulfide, rotten eggs Carboxylic acids Propionic acid, sweat Butyric acid, rancid dairy or puke Valeric acid, smelling of dirty feet Caproic acid, smelling of cheese and goats Aldehydes (e.g. butanal) Amines Triethylamine, old fish Ethanolamine, unpleasant Putrescine, rotten meat Cadaverine, rotten meat Heterocyclic compounds Indole, smelling of feces Skatole, smelling of feces Standard bathroom malodor The US Government Standard Bathroom Malodor, said to be one of the worst-smelling substances,