I had seen The Exorcist before, but it was an even more disturbing experience to watch it frame by frame. That’s what my friends and I did in the early 1990s, when we were high school students working on a class project about the history of subliminal messaging in media.

We adjusted the levels on the most sophisticated stereo we could find to isolate that part at the very end of the Beatles’ “Strawberry Fields Forever” where a distorted voice supposedly says, “I buried Paul.” A generation before us, that short clip of audio fortified conspiracy theories that Paul McCartney (still with us today) had actually died in 1966. We studied a 1973 book called Subliminal Seduction by Wilson Bryan Key, about how covert messages could be deployed as sales tools. The five of us struggled to find the nude figures he claimed were hidden in the ice cubes of old liquor ads. (And some of us were really looking.)

We also went to the video store to rent a copy of The Exorcist, which had long been rumored to contain subliminal imagery aimed at disturbing viewers in ways they could never fully comprehend. We tried to go frame by frame through the 1973 demonic-possession film, or at least moment by moment, as painstakingly as the crude tech of pausing and unpausing a VHS player would allow.

Then we found something. The young priest Father Karras (played by Jason Miller) has a dream about his recently deceased mother descending the steps into a subway station with an agonized expression on her face. We Catholic school kids understood what that represented—a descent into hell, no doubt. But that was symbolism, not subliminal-ism. In the midst of that sequence, however, comes a split-second flash followed by the momentary appearance of a horrid white face, sneering with decayed teeth, eyes pooling in red sores. It’s terrifying—but barely perceptible.

The face appears for only a handful of frames, and while that might be enough for a viewer to briefly register the image, it’s not long enough for one to actually grasp it. Moviegoers in 1973 would have been left unsure about what, if anything, they had just seen, creating fertile ground for terror. We counted that as proof that there really were subliminal techniques at play in The Exorcist.

While that pallid demonic face is unnerving, it’s also clearly a person in makeup, deliberately slipped into the edit. But as we continued to parse the movie, we found something our minds couldn’t explain as easily.

It happens about 49 minutes into the film, when the possessed young girl, Regan (played by Linda Blair), thrashes on her bed as a team of doctors visit her home. Her eyes roll back and her throat bulges grotesquely (both effectively creepy makeup effects). Then she vaults onto her feet, hauls back her hand, and knocks one of the approaching doctors across the room.

There are a lot of rapid cuts in the sequence, and as we paused and unpaused, looking for hidden images, we saw the young girl’s face suddenly distort. Her eyes became fathomless black pits, her hair appeared to curl into horns, and her face suddenly became more stoic and imposing. We halted on the image, staring at those empty sockets.

It didn’t look like a makeup effect. There was no discernible editing cut either. It just appeared that her face…changed. Right in the middle of the shot. We took a picture of the screen with a camera, and one of my friends reached out to stop the tape. We were deeply freaked out.

We had seen digital morphing effects used for things like Michael Jackson’s “Black or White” music video and the silvery liquid shape-shifter in Terminator 2: Judgment Day, but that technology didn’t exist when The Exorcist was made. It felt like we had gone hunting for a clever trick and discovered something inexplicable, or maybe otherworldly. Sitting in our friend's basement on a dark winter night in Pennsylvania, we debated whether the real face of a demon could manifest in something like a film.

Our minds spasmed in all sorts of bizarre directions. One of us ejected the tape from the VHS player. I remember my friend saying he wanted it out of his house.

That was 30 years ago. I don’t really believe in supernatural phenomena, and any notion that we had witnessed an actual satanic cameo now seems absurd. It probably felt ridiculous to us even then, once the spell of the movie had lifted. We were kids who had allowed a legitimately scary film to get under our skin and into our heads.

I knew I had seen something, however, and in the decades since, I’ve sometimes wondered whether it was an accidental image or something created intentionally by the filmmakers to instill an unconscious moment of dread. Or maybe…it was just the tape? VHS was notorious for its poor fidelity, so it seems possible that some of the distortion could have been the result of that format’s innate fuzziness.

I recently opened The Exorcist on the Max streaming service and made a slow-motion recording of the scene in question. Part of me expected not to find anything. But then, right where I remembered it, there was the horrid, eyeless face—now in HD.

The movie’s director, William Friedkin, died this past August, just a few weeks shy of his 88th birthday. But in October 2012, I interviewed him onstage at a post-screening Q&A for the movie, and used it as an opportunity to ask my long-held questions about The Exorcist’s hidden effects.

I had told this anecdote about the VHS tape and the school project to one of the event organizers, and they must have passed it along to Friedkin, although not entirely accurately.

“Another thing that’s often said or speculated about, with this movie, is that you used subliminal techniques to unsettle the audience,” I began.

Friedkin rolled his eyes and became immediately hostile in front of the crowd. “I know … You wrote some bullshit book about that. Go ahead and explain yourself,” he said.

I told the real story, explaining that it wasn’t anything nearly that professional. I had assumed he would have no problem clearing up years of widespread speculation, but Friedkin seemed annoyed by such conjecture. Looking back, maybe he was irked in the way a magician might be if you ask what’s up his sleeve.

After his initial dismissal, Friedkin basically confessed. But not to everything.

“The first time I ever saw subliminal perception used in a film was a great documentary by a French filmmaker named Alain Resnais,” Friedkin said. “He made a documentary called Night and Fog, and it’s about the concentration camps. What he did was he showed in color these beautiful long tracking shots of the weeds and wildflowers that had grown over Auschwitz and two or three of the other camps…. You’d see long tracking shots of a peaceful setting, and there was a narrator’s voice talking about what happened in the camps, and then suddenly there would be these quick black-and-white shots of the dead bodies all piled up, of what had happened in the extermination camps. It was the first time I had ever seen that effect in a film. It was in the middle ’50s.”

Friedkin noted that Resnais did this again in 1959’s Hiroshima Mon Amour, about a European woman who falls in love with a Japanese man, both of them scarred by the events they experienced during World War II. “They were in bed together, and there would be these quick shots of the bombing of Hiroshima,” Friedkin said. “It occurred to me that what he was doing, this technique that he had discovered, was the way we think. You’ll be doing something at your desk or somewhere and a thought will flash into your mind, or an idea or a face, that has nothing to do with what you’re involved with at the moment. Don’t you sometimes have that happen?”

I told him I did.

“We all do, I think,” Friedkin said. “There’ll be a flash, either a thought or an image, and Resnais discovered how to use that in cinema. It was a knockout…. I just took that idea and put it in The Exorcist.”

“So it is there?” I asked

“Oh, of course it’s there,” Friedkin replied.

“You were making it out like I was making this up,” I told him.

Friedkin was smiling at that point. Devilishly, it seemed. He copped to inserting the grimacing pale face glimpsed during the Karras dream sequence. “What’s used there, those quick shots, were the tests that [makeup artist] Dick Smith did on Linda Blair’s double (Eileen Dietz),” he said. “She had an all-white face and red lips, and I didn’t like it as the makeup for the demon, but viewed that way, as a quick cut, it’s very frightening. I took those pieces, maybe three frames, sometimes two frames. Two frames is one twelfth of a second, and three frames is an eighth of a second.”

“Not easy to catch on a VHS tape,” I said.

“Well, you couldn’t catch it before VHS, though,” Friedkin said. “Now you can stop the DVD and stare at it.”

I asked if there were more flashes like that, apart from the pale face. Friedkin admitted to “subliminal sounds, impressionistic sounds,” like the buzzing of bees. “That was me,” he said. “I took a lot of different disturbing industrial sounds and played them way off in the distance."

We never resolved the question of whether the black-eyed face I saw in the slapping scene was an intentional addition. There aren’t many left now who would know for sure.

“I knew that was going to be the first question.”

So said Norman Gay, who 50 years ago was part of the four-member team who would go on to share an Academy Award nomination for their work editing The Exorcist. Two of those editors, Evan A. Lottman and Jordan Leondopoulos, have since died, and Bud S. Smith, credited for the movie’s Iraq sequence, did not reply to an interview request by press time.

Gay, like Friedkin, had heard a lot about the so-called subliminal edits in The Exorcist. He was braced to talk about the matter once again. “I never saw that in it at all,” he said. “My belief is that, if it were there when I was working on the movie, I would’ve heard about it, because everyone told everybody whatever was happening.”

Gay had previously worked with Friedkin on The French Connection, and did not edit the Karras dream sequence or Regan’s slap of the doctor. “I did a lot of the reediting of the opening, which is a very mysterious sequence that takes place in Iraq, and I cut a lot of the sequences with Lee J. Cobb and Ellen Burstyn. And I killed off Max von Sydow, the exorcist. I gave him a heart attack…. Those are the ones I remember spending a lot of time on.”

He doesn’t believe The Exorcist contains material that is truly subliminal, existing below the possibility of perception. “None of us ever talked about anything secretly that we were trying to do or asked to do,” he said. “At that time, I think that a concept of subliminal editing was kind of in the air. I think they were accusing commercials of doing it all the time, and I don’t hear anybody talking about that anymore.”

Instead, the images that casual viewers might call “subliminal” are really just rapid breakaways, which actually are visible, albeit briefly. They create a destabilizing effect since they don’t register long enough for the viewer to fully comprehend them. “I would call them ‘quick cuts,’ but you didn’t use them in most standard films because there was no need for them,” Gay said. “This is a film that is trying to catch you by surprise.”

Nothing about The Exorcist felt especially otherworldly to Gay as he worked day by day, piecing together multiple takes and seeing footage of behind-the-scenes work. “People I’ve met who were young, probably your age, saw it and told me they couldn’t sleep for days or they were scared to death. And I can’t understand that at all,” he said. “I was working from the inside out. It’s just like, nobody can understand how her head turns around. But it was a dummy!”

Looking at the slow-motion footage of the doctor slap, as the little girl’s eyes suddenly darken and her face seems to stiffen, Gay couldn’t definitively rule out that the frame was doctored. “If it is intentional, it could represent the demon taking possession of Regan,” he said. “I have never seen any of the film in such slow motion and blown up like that.”

He added that it was probably not caused by an actual editing splice; the face is too smooth and subtle for that. “It was just physically difficult to create that kind of one-frame, two-frame thing, because you had to cut up the film and then you had to paste it back together again,” he said. “Now you don’t have to cut anything. You can reduplicate any shot as many times as you want because of digital editing.”

Gay’s verdict: blame wardrobe. “It appears to me that what we are seeing is a piece of her nightgown that has been blown into the air. It may have been done by a wind machine effect of some sort,” he said. “I don’t think it is an edit because you can see the parts of the nightgown in the next shot.”

The disturbing nature of The Exorcist’s story, he concluded, leads people to project outlandish ideas onto it. “You hear this about a lot of films, all the coincidences,” he said. “I was just looking at something on the internet about all the bad things that happened on Rosemary’s Baby.”

When dealing with a possible demon infestation, it’s best to turn to experts for help. I found two to examine the footage and offer their own explanations of the frightening face that appears to take over the young girl.

If it was a deliberate visual effect, it was a remarkably simple one, said Dana E. Glauberman, whose credits include dramas such as Up in the Air and Creed II, as well as VFX extravaganzas like The Mandalorian and the recent Ahsoka series. She also has supernatural cred, having edited Ghostbusters: Afterlife.

“I’d say her face does change…well, maybe not her entire face, but just her eyes,” Glauberman said. “I think it very well could have been done in color timing, where they darkened the area around her eyes for just those couple of frames.”

It’s so subtle and goes by so quickly, however, that if it was intentional, it was a very small adjustment. “I’d say it’s one frame of a change,” Glauberman said. “There very well could be a jump cut in there right after her eyes go dark, but the one frame looks like her eyes and her facial expression too. I’m shocked that you actually noticed that as a kid!”

Todd Vaziri, a veteran visual effects artist and historian who has written extensively about vintage filmmaking techniques, agreed with Gay’s assessment that the “demon” hidden in this shot is really just a trick of the light from her nightgown and movement.

“I’m looking at your shot and I’m stepping through it, and I’m going to say that for the first part of the shot, you can see that her screen right eye is in shadow. She’s self-shadowing. Her brow is blocking the key light,” Vaziri said. “Then for one frame, it looks like both eyes now are completely black, and it’s a little…” He pauses, then laughs. “I’m just hanging on this frame and it’s freaky as hell.”

Freaky, but most likely accidental, according to Vaziri. “This seems to me like just a lighting issue,” he said. “Her natural movement moved both eye sockets for one frame out of the key light. And that’s the effect.”

Glauberman disagreed, maintaining that the change in Regan’s appearance is too stark. She thinks Friedkin must have darkened the sockets in that one frame. “It’s too perfect,” she said. “If she was just covering the light, why would the shadow be over her eyes and not her whole face?”

Vaziri, though, is sticking with the fluke theory. He believes you could probably find similar distortion in lots of movies, but it stands out in this case because The Exorcist is so disturbing. “This is not an abnormal thing. This happens all the time,” he said. “When great masterpieces exist, we put them under a microscope—especially when the movies have such lore as The Exorcist. The conspiracy theories and the mythology—you can’t control it.”

Maybe for once, the devil was actually not in the details. It’s a testament to the enduring power of The Exorcist that a single frame can still leave people unsettled half a century later.