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.'