Why animals die from eating poisonous plants
Utah State University Extension
Behavioral Education for Human, Animal, Vegetation & Ecosystem Management
If animals can learn which plants are toxic and which are safe, then why do they eat poisonous plants and die? Under most circumstances animals can learn if a plant is safe or harmful because eating results in feedback from the gut to the brain. Feedback tells the body whether or not a food is safe. Unfortunately, in some situations this mechanism for identifying harmful foods is circumvented causing animals to suffer from overingestion of poisonous plants.
Burritt, Elizabeth A., "Why animals die from eating poisonous plants" (2012). Wildland Resources Faculty Publications. Paper 1534.