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Continuity mistake: In the underground bunker Carol and Dr. Marvin listen to the aliens voice from the slowed down tape recorder. At first we see the tape in the middle of the spool than ten seconds later it jumps to the end. (00:25:45)

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Question: What happened to the movie that Chris was shooting. It just disappears from the script after Burke Dennings dies?

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Question: Who put the cross under Regan's pillow? It couldn't be the demon. (01:12:35)

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Continuity mistake: After the first part of the exorcism Father Karras sits on the steps as Father Merrin walks to the bathroom. His coat and purple scarf are draped across the railing but two shots later as Father Karras goes back into Reagan's room the items have disappeared. (01:54:45)

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Audio problem: Dr. Marvin watches the magnetic interference unit take down an alien spaceship and says, "…saucer hit and down in the Potomac". If you look closely his lips do not match what we hear. (00:13:10)

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Continuity mistake: As the aliens announce their intentions to the people of earth Dr. Marvin walks up to a radio in the back of the lab and says, "If I'm right they'll sail into Washington in broad daylight…". If you look closely the radio is pointing to a different station that it was when we saw it previously in the scene even though no one has gone near it. (01:04:35)

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Continuity mistake: After the aliens announce their intentions Dr. Marvin and the generals meet together back at the Pentagon office. Dr. Marvin's hanky in his jacket pocket is arranged differently between shots. (01:07:05)

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Continuity mistake: Damien goes back into Reagan's room and takes the towel on the night stand to her right and wipes her forehead with it. He never puts it back on the nightstand but when Father Merrin comes back into the room it's there again. (01:56:15)

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Visible crew/equipment: During the final attack after Carol falls on the floor in a hallway in the Pentagon there's a shot of a crowd running towards the camera. The woman in the front has the shadow of the boom mike right on her forehead as she comes close to the camera screaming bloody murder. (01:13:25)

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Continuity mistake: After the first part of the exorcism, Father Merrin leaves Regan's room and we see his red prayer book and crucifix sitting on the nightstand as he does. He sits on the steps and then goes into the bathroom to take a pill, but later as he goes back into her room he has the book and crucifix in his hand. (01:53:00)

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Deliberate mistake: After the aliens announce their intentions Dr. Marvin meets with Carol back at their hotel room. He tells her that she must take a flight alone back to Palm Springs and then leaves the room. In the end of the scene she picks up a copy of The Evening Star, which is an obvious prop as it has no date on it. (01:08:50)

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Continuity mistake: Father Dyer runs to Chris' car at the end of the movie as we see another car coming at them and passing on their left. In the next shot that car has disappeared. (02:05:25)

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Continuity mistake: As Regan spins her head around her blue nightgown is now totally clean. (01:49:50)

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Deliberate mistake: Father Merrin says, "It is He who commands you", and we hear and see the ceiling crack above his head. In the next shot we see the ceiling above him and they are no cracks in it, but four shots later we see the exact same spot and now cracks appear even though we hear no more cracking over-dubs after the first one. (01:49:15)

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Continuity mistake: Father Merrin says, "I cast you out", and the green vomit that was around her mouth has now disappeared. (01:49:05)

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Continuity mistake: Father Merrin says, "Be gone" as he walks over to the other side of Regan's bed, and the lamp on her right almost falls over. In the next shot it's not moving at all. (01:49:25)

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Continuity mistake: Father Merrin says, "Hear my prayer" as he puts his hand on Regan's head. If you look closely the vomit first comes out when her head is facing the right and it totally soils her blue nightgown. In the next shot with her head facing left there's nothing on her blue nightgown. (01:48:05)

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Continuity mistake: Father Merrin says the Lord's Prayer as he stands at the edge of Regan's bed. At first she's sticking her tongue out at him then in the next shot she's not. (01:45:20)

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Continuity mistake: Father Merrin prays with his Rosary Beads as Chris brings him a cup of coffee. At first the cross is up near his hand but in the next shot it's dangling close to the floor. (01:41:55)

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Continuity mistake: Back at his apartment Damien plays the tape of Regan backwards again on his tape recorder. Some items on the 1st and 2nd shelf on the back wall are rearranged between shots. (01:35:55)

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