An anonymous reader writes "Ratting someone out' just became much more literal. Dutch police are using trained rats to help keep the streets clean. 'Detective Derrick and his rat partners cost just £8 each and are capable of being trained to identify an impressive range of odors—including drugs and explosives—within ten to 15 days. In contrast, a police dog costs thousands of pounds and requires a minimum training period of eight months. The training procedure is straightforward: the rats are kept in a cage with four metal tea strainers attached inside, one of which contains gunpowder. When the rat recognizes the smell, it is rewarded with a "click" and a small treat. Eventually the rat will learn to move towards the smell instantly. In a demonstration it takes Derrick just two seconds to locate the offending odor."