If you have seen the movie The Exorcist, you might remember the words of advice that Father Merrin speaks to Father Karras, while they are putting on their vestments and readying their things, before they enter the bedroom of the little girl, Regan, who has been possessed by a demon and who the two priests intend to help, by way of an exorcism. “He’s a liar,” Father Merrin says. “The demon is a liar. He will lie to confuse us. But he will also mix lies with the truth. To attack us. The attack is psychological. And powerful. So don’t listen. Remember that. Do not listen.”