the formation of associations between elements or occurrences after only one exposure to them. The term is discussed most commonly with reference to conditioned taste aversion and conditioned fears. For example, a person who becomes sick after one meal at a restaurant and subsequently refuses to dine there has formed a negative association between the illness and that one meal. Similarly, a dog with no previous aversion to nail trimming may suddenly become fearful of the procedure after having its nails cut painfully short. The precise neural mechanisms by which such rapid and often long-lasting associations are formed have yet to be determined.