Continuity mistake: Father Merrin walks over to see what the other archaeologist has found at the dig site and the items in the sifter move between shots in the close-up. (00:03:15)
Continuity mistake: At the dig site in the beginning of the movie, the items on the rock behind Father Merrin move in the close-up after the other archaeologist shows him what he has found. (00:03:25)
Continuity mistake: Father Merrin watches three metal smiths working and the piece of metal on the anvil is red hot in one shot and not in the next. (00:05:45)
Continuity mistake: In the archaeologists office at the beginning of the movie Father Merrin looks at the clock on the wall as it stops. The first time we see it the pendulum is to the left of center but the second time we see it, it's dead center and it hasn't been touched. (00:06:45)
Continuity mistake: The phone on the right of the archaeologist's desk moves between shots in the close-up. The first time we see it the connector chord is flush with the desk but the second time we see it the chord is above the desk and no one goes near it. (00:06:45)
Continuity mistake: When we first see her, Chris MacNeil lays in bed editing her script. The lamp above her head changes position between shots after she turns it on. (00:10:50)
Continuity mistake: Chris picks up a newspaper as she tells Carl, "We've got rats in the attic". In the next shot the newspaper is unmoved. (00:12:40)
Continuity mistake: Chris says to Carl, "We've got rats in the attic" and he replies, "Rats?". All the items on the table to her left have been rearranged between shots as she turns towards him. (00:12:40)
Continuity mistake: At the movie set, Chris says to Burke Dennings, "It just doesn't make sense" and the guy in the blue shirt in the background is standing up. In the next shot he's bending over. (00:13:20)
Continuity mistake: At the movie set, Chris yells, "Hold it, hold it" as Father Karras watches and walks away. In the next shot several extras along with the line of shade behind him disappear. (00:14:50)
Continuity mistake: After returning home from the movie set Chris walks in and says hello to Sharon. The bottle of Coke, the typewriter carriage and the page she is typing all move between shots by the time Chris gets to the desk. (00:16:10)
Continuity mistake: After returning home from the movie set, Chris' necklace is tucked under her collar. She doesn't go near it but two shots later it's over her collar. (00:16:30)
Continuity mistake: After returning home from the movie set, Chris gets a letter from the White House which she reads with both hands. Regan says, "Hi Mom" and in the next shot Chris has a drink in her hand. (00:16:35)
Continuity mistake: After Chris returns home from the movie set, items on the window sill, the flowers on Sharon's desk and the pencils in her pencil holder all move inbetween the two close-up shots of her as she sits at her desk. (00:16:50)
Continuity mistake: Chris and Regan walk back to Sharon's desk and the radio on the shelf to the right of the desk has moved between shots. (00:17:20)
Continuity mistake: As Father Karras goes to New York to see his mother a woman in yellow on the sidewalk with her two children disappear between shots as he crosses the street. (00:18:30)
Continuity mistake: Before Father Karras walks into his mother's apartment the lights are on. In the next shot as he walks in the lights are off and he turns them on. (00:19:10)
Continuity mistake: Father Karras eats dinner in his mother's apartment and the curtain on the far side of the table moves without being touched the second time we see it. (00:20:25)
Continuity mistake: Father Karras bandages his mother's leg and we see her right hand as she raises it and he says, "Mama, I could take you somewhere ". In the next shot she raises her hand to her head and she now has a band-aid on her wrist. (00:20:50)
Continuity mistake: In the scene in their basement Chris takes the painted bird from Regan who touches the wood post in the center of the room with her right hand. In the next shot she's leaning against it. (00:22:15)
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