Answer: Conditioned taste aversion is a strong Pavlovian dislike of a flavor.
Conditioned taste aversion (CTA) is a behavioral phenomenon that results in a severe dislike of a flavor after an animal gets sick from that flavor. It is often such a powerful behavioral response that even a single pairing between the offending stimuli and sickness can result in an aversion that persists for years.
In terms of Pavlovian learning, the toxic food is the unconditioned stimulus and nausea is the unconditioned response. Following the onset of illness, the nausea in response to presentation of the food becomes the conditioned response.
We believe that CTA is an evolutionarily preserved protective mechanism. Consider an ancient prehuman ancestor. They would forage for foods, and some of those foods would contain toxins. As nausea and vomiting may occur as a result of eating those foods, the CTA may then be established. This would be a powerful reminder to the animal that the particular food should be avoided at all costs. A hominid without this ability to learn may be less viable if they continue to eat toxic foods.