Chemical warfare is widely practiced in the animal and plant kingdoms. Just as microorganisms produce antibiotics that inhibit the growth and reproduction of competing organisms, more complex plants synthesize chemicals that render them unpalatable to potential predators or that are truly toxic, thus selecting for individuals that avoid them, or producing aversive reactions that limit consumption to once or twice only. Occasionally, however, these plants accidentally enter the food chain of livestock or humans, directly or indirectly, leading to a toxic reaction.