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[Morrigoon]

If you overlay two maps of medieval Europe, one showing major areas of witch burnings, and another of major rye growing areas, you will find a near perfect match.
In "The Crucible", the description of Tituba making a "witch cake" describes her making it with rye. Ergot poisoning (ergotism), which comes from consuming rye stricken with the fungus ergot, has the following symptoms (courtesy of wikipedia):

Convulsive symptoms
Convulsive symptoms include diarrhea, paresthesias, itching, seizures, headaches, nausea and vomiting. Usually the gastrointestinal effects precede CNS effects. As well as seizures there can be hallucinations and mental effects including mania or psychosis. The convulsive symptoms are caused by clavine alkaloids.

Gangreneous symptoms
The dry gangrene is a result of vasoconstriction induced by the ergotamine-ergocristine alkaloids of the fungus. It effects the more poorly vascularized distal structures, such as the fingers and toes. Symptoms include desquamation, weak peripheral pulse, loss of peripheral sensation, edema and ultimately the death and loss of affected tissues.

Which is similar to the claims of witch burners against the accused.