You believe in werewolves and you see a sign of one. Then you 'know' that a werewolf has passed. An adequate signifier is evidence found where it has killed. In a pre-rational culture a psychopath might violently murder someone. Then villagers will attribute the incomprehensible horror to a monster, like a werewolf.
One bloody murder is committed by a psychopath. Another is done by a real pack of wolves. A myth is generated in talk and later from the memories of villagers.
In both instances this myth frames a vision of the footprints of men and the footprints of wolves. Seen together in the sun hardened mud, both prints signify one foot of the same beast. Together they show evidence of the werewolf's contortions and the agony of its transformation to wanton killer.
Both murder by the psychopath and by wolves becomes one seemingly unmotivated act by the same monster. Villagers interpret the signs as cultural units that give birth to the myth. It is real, at least as such. The three images in Photographic Evidence found on the left record such an event.