Even if mental illness isn’t contagious, sometimes the symptoms are, as people start to believe that something is happening to them because it is happening to others. Throughout history, we find accounts of bizarre beliefs or behavior that grew out of hand when more and more people joined in. Sometimes the “epidemic” would spread from town to town, or even through mass media. Such was the case for the Meowing Nuns.
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.
Mass hysterias are not limited to isolated groups, though, or even people under stress. And it can happen anywhere, at any time. The newest of the ten cases at How Stuff Works is from 2006! And it probably won’t be the last.