During the Middle Ages, many nuns were forced into convents by their parents and often stressed by a lifestyle not of their own choosing — one that demanded celibacy, poverty and hard manual labor. Two especially bizarre cases of mass hysteria involved meowing and biting nuns.
In the first case, a nun in a large French convent began meowing one day. Soon others joined in, and eventually every nun in the convent was meowing. The noise became structured; all of the nuns would meow together for several hours at the same time every day. The neighbors could hear the collective caterwauling and were understandably annoyed. Eventually the nuns quieted down after being threatened with a beating by soldiers.
Next door in Germany, in the 15th century, a nun began biting the other sisters in her convent. It wasn't too long before all of the nuns were biting one another. Word spread about the biting nuns, presumed to have caught some type of nefarious infection, and soon the "infection" spread to convents throughout a large portion of Germany, mostly in Saxony and Brandenburg. But it didn't stop there; convents in Holland and even Rome were also affected [source: Bartholomew and Goode]. The nuns eventually stopped biting because of exhaustion [source: Wundt].