Convulsive ergotism is characterized by nervous dysfunction, where the victim is twisting and contorting their body in pain, trembling and shaking, and wryneck, a more or less fixed twisting of the neck, which seems to simulate convulsions or fits. In some cases, this is accompanied by muscle spasms, confusions, delusions and hallucinations, as well as a number of other symptoms.
It has been suggested that the cause of the plague was ergotism, which results from consuming ergot-laced bread. Ingestion of ergot, a psychotropic mold that grows on rye, can lead to delirium, hallucinations, and seizures, as well as other symptoms. While today this is called ergotism, contemporaneously it was known as "Saint Anthony's fire". However, another symptom of ergotism is loss of blood supply to the limbs, making coordinated movement like dancing difficult; as such, Waller considers it to be an unlikely cause of the plague.