June 24, 1374 - On this day was a very strange thing happened in Aachen, Germany. Hundreds (maybe thousands) of the city's citizens suddenly started dancing in the streets. No, this was no coordinated flash mob or a bunch of drunks prancing around a maypole. These people were whacked out nutters who writhed and twitched until they collapsed and foamed at the mouth.
Dancers later spoke about wild hallucinations and encounters with giant spiders. Others related the experience to a religious awakening. Whatever the case, it wasn't a local phenomenon - outbreaks like this would pop up all over Europe between the 14th and 18th centuries.
Nobody is sure about what may have caused these bizarre outbreaks, but one theory is that ergot poisoning was at the root of the madness. Ergotism is a condition caused by eating rye that is infected with a particularly wacky fungus. It's the same fungus that many believe caused the bewitching behavior at the root of the Salem witchcraft accusations.