What is ergotism in relation to witchcraft?

Ergotism is a condition caused by the ergot fungus. This grows on grains and causes hallucinations, convulsion, paranoia, and mania. Before people had the technology to store most food safely, stored grain would be contaminated by this fungus, and everyone who ate it would get sick without knowing why.

In 1976 Linda Caporael published an article in Science magazine which speculated that the Salem witch trials were actually due to ergot poisoning in the village. The symptoms that the Salem villagers described as being the result of witchcraft were some of the same symptoms that you get from eating ergot.