 The behavior spreads rapidly and broadly in an epidemic pattern.This kind of comportment could have been caused by elevated levels of psychological stress, caused by the ruthless years (even by the rough standards of the Middle Ages) the people of Alsace were suffering.Waller speculates that the dancing was "stress-induced psychosis" on a mass level, since the region where the people danced was riddled with starvation and disease, and the inhabitants tended to be superstitious.