Continuity mistake: In the scene in their basement Chris brings the Ouija board over to the ping pong table and Regan puts the paddle down with the ball underneath. In the next shot the paddle is there but the ball disappears. (00:22:45)
Continuity mistake: As Chris and Regan discuss how to play the Ouija board the pointer is to the right of the word No. In the next shot when Regan picks it up it's covering the word No. (00:23:10)
Continuity mistake: In bed Regan reads "Photoplay" magazine as Chris touches the covers of the bed. In the next shot she's pulling the magazine away from Regan. (00:23:30)
Continuity mistake: Chris talks to Regan as she puts her to bed. If you look closely the large pictures on her night table change position throughout the scene. (00:23:45)
Continuity mistake: Father Damien and Tom have a drink at a local bar where Damien confides that he has lost his faith. When he brings the beers over both glasses are full but several seconds later when he takes his first sip the head is already gone. (00:26:50)
Continuity mistake: Before Chris goes up into the attic to see what's making the noise Regan is wearing a blue nightgown. A few seconds later they cut back to her and she's wearing a pink nightgown. (00:28:30)
Continuity mistake: As Chris goes up into the attic to see what's making the noise, the flame on the candle gets longer between shots as she walks up the steps. (00:29:45)
Continuity mistake: As Chris walks around the attic to see what's making the noise more candle wax appears dripping down its side between shots. (00:30:00)
Continuity mistake: After Chris is startled by the exploding flame in the attic there's a shot of a priest caring flowers into the courtyard of a church and if you look closely the flowers on the right are the same in the close-up but the flowers on the left are not. When he walks into the chapel the flowers are rearranged again. (00:31:20)
Continuity mistake: After Chris is startled by the exploding flame in the attic there's a shot of a priest carrying flowers across a courtyard into a chapel. When he first opens the door to the chapel he's in the shade, but when we see him walking into the chapel from the other side of the door the sun is shining. (00:31:30)
Continuity mistake: In Doctor Klein's office the handle on the ice bucket in the back of the room under the blue picture is moved as the scene progresses and Chris talks to the doctor. (00:33:45 - 00:35:55)
Continuity mistake: Chris takes Regan to Doctor Klein for some tests to see what's wrong with her. As she sits in the office waiting for the doctor to come in, the papers on his desk move between shots without anyone going near them. (00:34:10)
Continuity mistake: As Chris sits in the office waiting for Doctor Klein to come in, the tissue coming out of the Kleenex box behind his desk moves between shots without anyone going near it. (00:34:15)
Continuity mistake: As Damien walks into the psychiatric ward to visit his mother the woman directly across from her changes sides on her bed between shots. (00:38:15)
Continuity mistake: Sitting in front of the fireplace at her party, Chris asks Father Dyer, "Who's the priest I keep seeing thereĀ " and the woman to his left has a drink in her hand. In the next shot the drink is on the table. (00:40:20)
Continuity mistake: Sitting in front of the fireplace at her party, Father Dyer tells Chris that Father Karras' mother had died the previous night. The candle in the candleholder to her right rotates throughout the scene. (00:40:35)
Continuity mistake: At the party, a drunk Burke Dennings calls Karl a, " Bloody, damned, butchering, Nazi pig!" and the chain around his eyeglasses moves on his chest twice between shots. (00:40:45)
Continuity mistake: At the party Father Dyer sings just before Regan walks in and says to the Astronaut, "You're gonna die up there". The music book on the piano is open to the same page but the manuscript paper underneath has been moved between shots. (00:42:35)
Continuity mistake: Throughout the film it has been made clear that it's Autumn and it is cold. Leaves have fallen and they are crunchy on the ground. In the scene where Father Karras is walking with the detective they turn a corner and it's summer again. The sky in the scene goes from grey to blue and the trees have re-greened as they pass a tennis court with players in their short whites. (00:43:00)
Continuity mistake: After Regan walks in and says to the Astronaut, "You're gonna die up there" Chris gives her a bath. When we first see them she's sponging her down with her right hand and soapy water. In the next shot she's using her left hand and the water is clear. (00:43:20)
Answer: The demon wants everyone to lose hope for the girl and give up on her. Her father, having already flown the coop, just makes this goal that much easier.
TonyPH