Whether or not it's true is still under debate, but there is a theory that poisoning from the ergot fungus may have kicked off the Salem witch trials.
The events of the Salem witch trials, which resulted in the executions of twenty men and women, began with eight young women becoming afflicted with "distempers." "Disorderly speech, odd postures and gestures, and convulsive fits" characterized their unusual condition.
The "distempers" were eventually blamed on witchcraft, but some researchers point to a much more ordinary cause. Convulsive ergotism—an illness resulting from the consumption of rye infected by ergot—causes many of the girls' reported symptoms, including painful muscular contractions, convulsions, and hallucinations. (The hallucinogenic drug LSD was originally synthesized from ergot).
Another form of ergotism shows up even earlier in history. In the middle ages, bread made from ergot-infected rye lead to accumulation of dangerous chemicals in the bodies of those who ate it, causing gangrenous ergotism. Gangrenous ergotism makes body parts flaky and dry until they eventually fall off. A thousand years ago, when gangrenous ergotism reached epidemic proportions in Europe, it was called St. Anthony's Fire.
Although the consumption of ergot by farm animals is still a concern, today there are very few cases of ergotism among humans. In fact, medications derived from ergot have since been used as effective treatments for migraine headaches and Parkinson's disease.