The Element Encyclopedia of Witchcraft: The Complete A-Z for the Entire Magical World - Judika Illes 2005
The term “skin-walker” refers to the same concept as those nahuals (sorcerers) who are able to change forms. It is the English translation of a Navajo term. Although traditional Navajo culture is shamanic, with a long tradition of magical healing and positive magical practices, the word “witchcraft” in Navajo is virtually always understood as malevolent. Use of the word “witch” almost always refers to a shaman gone bad or to a corrupt sorcerer or some sort of malevolent practitioner of magic. Traditional Navajo philosophy prizes harmony and places emphasis on the welfare of the community. Witches are understood to place individual desires above those of the group.
Navajo witches most frequently transform into wolves or coyotes. They may be distinguished from a regular wolf or coyote, at least by someone who is familiar with the genuine article:
Transformed wolves and coyotes may be unusually large.
They carry their tails in a different manner than real animals do.
They may betray themselves by wearing or carrying something associated with humans, like jewelry.