For millennia, people have debated whether it was possible for a human being to be possessed by an evil spirit. Stories of demonic possession date back to the Sumerians, who believed that diseases of the body and mind were caused by "sickness demons" called gidim or gid-dim. As recently as 1976, a priest was granted permission from a bishop to perform an exorcism on 22-year-old Anneliese Michel.

Is demonic possession real? Can the devil inhabit a human body? When a human being begins acting irrationally, irritably and downright evil, is it a case of the devil invading a person's body?

The answer is no. I have learned in my fieldwork that there is a perfectly good explanation for what appears to be possession.  And it is teething. If only Father Karras had given Regan some children's Advil and maybe a cold washcloth to chew on, a lot of heartache could have been avoided.