As Bagans explained for Dummies, it’s claimed that David started seeing visions of what he described as a “man with big black eyes, a thin face with animal features, jagged teeth, pointed ears, horns, and hooves.” He said he had recurring nightmares of this figure and suffered unexplained injuries such as scratches and bruises. Soon he said he was seeing this Devil figure during waking hours as well, invariably sitting in the family’s rocking chair. While only David saw the demon sitting in the chair, other family members claimed to have seen it moving on its own. When the Glatzels consulted a priest about David’s behavior, the boy is said to have begun hissing, spitting, speaking foreign languages, and quoting “Paradise Lost” (or so claim Ed and Lorraine Warren). The Warrens themselves were then called in to assist with the exorcism, and they claimed to have seen the chair moving on its own with David sitting in it, disappearing and reappearing in other locations in the house, and levitating.
During a final exorcism, Arne Johnson tells the demon to leave David and come into him, then Johnson is possessed and murders his landlord, then he goes on trial and becomes the first person to claim innocence for reasons of demonic possession, with the Warrens backing his claim. If this sounds familiar, it’s because this story was adapted for the plot of 2021’s “The Conjuring: The Devil Made Me Do It,” which adds a fictional Satan-worshiping witch and removes most of the stuff about the rocking chair for some reason.