The narcotics dogs are trained to detect the odor of controlled substances. These substances include marijuana, cocaine, methamphetamine, and its derivatives. Upon location of the odor of controlled substance, the dogs will alert to the smell. The dogs are trained to come to a final response of biting and/or scratching at the source of the odor. This is called an "aggressive" final response or active alert. This response may also indicate items recently contaminated with, or associated with, the odor of one or more of the controlled substances.