In a German convent near the River Rhine in the 15th century, a nun started biting her fellow sisters who, in turn, began biting other nuns. Soon, the convent was full of holy servants uncontrollably biting each other. From there, it spread to other convents throughout the region. Physicians at the time could find no medical reason to explain the bizarre behavior and it would be a while before the term “mass hysteria” was coined. The biting eventually subsided, but that wouldn’t be the last time a large group of people experienced a collective psychological episode, nor would it be the strangest. Not even close.

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