"A Tanzanian village was once overcome with contagious laughter so extensive that it shut down 14 schools."
On January 30, 1962, in the village of Kashasha, Tanganyika (now Tanzania), one group of students began laughing, and the laughter spread to more students, then beyond the school to the surrounding area, and from the area to neighboring villages. Though symptoms lasted a few hours or days, they also relapsed periodically; all in all, the episode lasted for about a year and affected several thousand people. One explanation for the incident, according to linguist Christian F. Hempelmann, is mass psychogenic illness -- a group response to constant stress, formerly dubbed mass hysteria. Similarly inexplicable group behaviors have been recorded throughout history, including the 1518 "Dancing Plague" in Strasbourg, during which dozens (and then hundreds) of people began dancing ceaselessly, some until they died of exhaustion.