Not to stray too far off of the topic, since we are staying to it so stringently, but there are medical facts that support the early descriptions of werewolves. People who suffered from a rare disease known as porphyria would have had symptoms that many would describe as lycantropy. Their teeth would have been misshapen, even jagged, and likely would have "glowed in the dark", which would have a been a frightening thought running into somebody like that on a dark country road at night, full moon or not.
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Then, too, there are accounts of Vitamin D-deprived people, living in the misty mountains in far northern countries during periods of very short daylight hours, who came down to the lowlands because they were driven to cannibalism as a way to remedy their nutritional shortfall.