I just read a World War II anecdote about botulism toxin being smuggled into China for use on Japanese officers by the resistance. To insure the plan would work, the local resistance tested the poison on donkeys, and abandoned it when the donkeys showed no ill effects. Ironically, the story went, donkeys are one of the only animals immune to botulism.
Is that true? Are donkeys immune to botulism? A quick google search brings up general warnings for all equines.