One bad meal can create a lifelong aversion, even hours before the sickness hit

John Garcia found that rats given flavored water, then made nauseous by radiation hours later, avoided that flavor for life - despite no pain and a delay that broke every rule of standard conditioning. Taste aversions form in a single trial because evolution wired animals to link sickness to what they ate, not what they saw or heard.

— John Garcia and Robert A. Koelling, Relation of Cue to Consequence in Avoidance Learning — Psychonomic Science, 1966