This idea that plants become desirable or aversive depending on their digestive consequences is simple. But, how do grazing animals figure out exactly which plants made them fee l good or ill? One way herbivores apparently accomplish this task is by regarding unfamiliar plants with caution. Animals associate positive or negative effects of nutrients or toxins with novel foods when offered meals that contain novel and familiar foods. When foraging bouts include several novel plants, plants that dominate the diet are probably 'weighted' more than less-consumed plants, even if the minor foods were primarily responsible for the positive or negative feedback. Furthermore, digestive feedback begins within 10 to 15 minutes of consumption which could help animals attribute digestive benefits or liabilities to specific plants. Finally, livestock grazing on rangelands usually become familiar with the forage resource and may seldom encounter truly novel plants. This allows greater opportunity to 'sort out' feedback from individual or similar groups of plants