Trance states, prophesying, convulsions, fasting, and other physical manifestations were often regarded as signs that a person was seized by spirits. In a book that sets out the prehistory of the early modern European witch craze, Nancy Caciola shows how medieval people decided whom to venerate as a saint infused with the spirit of God and whom to avoid as a demoniac possessed of an unclean spirit. This process of discrimination, known as the discernment...