According to ancient Greek folklore, a person could become a wolf (or werewolf) by eating wolf and human flesh together, while in later centuries, the causes varied between supernatural curses, conception during a new moon, sleeping in the light of a full moon and consuming specific herbs. In some cases, it was believed that merely drinking water that had been touched by a wolf would be enough to effect the transformation.
The moon has long been associated with mental health, or at least the deterioration thereof. Even today, despite a significant lack of supporting evidence, the belief that people act more deranged during a full moon phase survives.
It is thought that the folkloric notion of the werewolf may have been a manifestation of at the time unclassified medical conditions. Hypertrichosis, for example, causes abnormally thick facial and body hair growth, and porphyria, a sensitivity to light accompanied by symptoms of seizures and anxiety, may have been responsible for keeping people indoors during the day.
The folkloric belief in werewolves has been responsible for many executions in history — particularly during the Middle Ages when werewolves were considered the result of witchcraft. In Germany during the 16th century, for instance, Peter Stubbe was tortured and decapitated for his alleged use of a wolf skin belt to turn himself into a werewolf and kill people.