FATHER MERRIN: [to Father Karras] Especially important is the warning to avoid conversations with the demon. We may ask what is relevant but anything beyond that is dangerous. He is a liar. 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, Damien, and powerful. So don’t listen to him. Remember that – do not listen.
The Exorcist (1973), scripted by William Peter Blatty, directed by William Friedkin