The truth is, he used the sound of bees in some early sequences, which triggers an innate fear response in most people. You don’t know why you’re uncomfortable, but fight-or-flight is telling you something dangerous is near.
The buzzing of bees is a primal fear, but Friedkin said he also layered in “disturbing industrial sounds” in the background of the demon scenes, which also create a subconscious desire to back away from danger.
The most notable subliminal trick is the “white face” that flashes for just a fraction of a second during Fr. Karras’ dream sequence about his deceased mother. That face, pictured above, was never meant to be fully detected by the audience. “You couldn’t catch it before VHS,” Friedkin laments. “And now you can stop the DVD and stare at it.”
The face is that of Linda Blair’s stand-in, and the make-up was Dick Smith’s first proposal for the little girl’s demon appearance, before they settled on the mutilation motif. “She had all white face and red lips,” Friedkin said. “I didn’t like the make-up for the demon, but viewed as a quick cut, it’s very frightening.”
As for other images people purport to see in the film …? Friedkin says that’s just power of imagination.
Unless, as the Rev. Billy Graham proposed, the devil really did makes its way into some frames of The Exorcist.