Poison Shyness Among our behavioral similarities to other species are aversions, especially to poisons. It has been discovered in rats that withdrawal arises from an unpleasant experience. A pile of unfamiliar food on a rats' runway is first avoided; it is a new object. But eventually it is sampled. Afterwards, however, the food is again avoided, as if fear and curiosity are opposed. But the former gradually gives place to unhesitating consumption. If, however, the food contains a poison, such as zinc phosphide, the small amount first taken causes illness but may not be lethal. The rat then stops eating for a time. When it resumes, as a rule it refuses the toxic mixture; it has become bait shy. It may even reject separate constituents of the mixture with a distinct taste, such as sugar. Many people have had a similar experience. If we become ill after eating an unusual food, we avoid it afterwards, sometimes for years. Moreover, the aversion develops only when the ill effect is felt, perhaps for some hours. Source: the book "The Story of Rats" by S.A. Barnett