During the past 10 years, the study of learned aversions to foods has become one of the most' 'popular" areas of research in animal psychology. Learned aversions to foods are typically produced in the laboratory by first allowing an animal to eat (or drink) some distinctively novel substance and then making the animal' 'ill" in some way, most frequently by either giving it an injection of some "illness" -producing drug such as lithium chloride or by exposing it to a toxic dose of radiation. When an animal that has been treated in this way is subsequently given another opportunity to ingest...