Ergot is a fungus that can grow on rye and other grains, and it can cause a disease known as rye disease. Rye disease is caused by the ingestion of ERGOT-contaminated grain, which can lead to a variety of symptoms including hallucinations, convulsions, and even death. ERGOT has been known to cause epidemics in Europe since the Middle Ages, and it continues to be a problem in some parts of the world today.