Visible crew/equipment: When Cindy has her mom play the music box to see Rory, at the end the little girl jumps at her mother to scare her and jostles the camera. (00:00:25)
Continuity mistake: When looking at the dog from the bedroom window, there are 2 windows in the room facing the dog. When we see the window from outside only 1 window is lit up, despite both being in the same room. (00:11:30)
Other mistake: The clocks as we learn later in the film stop at 03:07 due to that being the time the witch died. However, the grandfather clock we see for the first time has stopped at 03:07. We then see it stop at 03:07 the next night too. However the minute hand is in a different spot to when it first stopped - it should have stopped at precisely the same point. (00:13:05 - 00:18:50)
Continuity mistake: When Rory throws the teddy onto the table its position changes when he runs outside to see why Cindy is screaming. (00:15:00)
Other mistake: When we first see the Warrens' home, the title card spells it Warren's. As it's the home of more than one Warren, the apostrophe should be at the end. (00:15:30)
Continuity mistake: When Rory sees the porch door open by itself it is wide open. When he approaches the door, it is only ajar. (00:21:15)
Continuity mistake: When April and Carolyn are playing Hide and Clap, the blindfold on Carolyn keeps moving. Note the amount of skin visible above the blindfold and under the hairline. (00:25:30)
Factual error: The moving truck that transports the Perron family's belongings didn't exist in 1971. It is a 1973 model or newer.
Visible crew/equipment: When they are performing the exorcism at the end, there is often a white marker by the rear right (viewer left) chair leg.
Factual error: The morning after the exorcism, the headlights on all the cars outside of the house are still on. There is no way car batteries from the 1970s would have lasted all night.
Continuity mistake: After being chased in her house, Judy closes the door to the bedroom and proceeds to put her hands on her ears, underneath her hair. The very next shot, she still has her hands on her ears, but it is over her hair.
Continuity mistake: When Lorraine sees Rory in the music box mirror, the items on the wall should be reversed, since it's a mirror, but they are not. When she turns around to look, everything is in the exact same position.
Answer: It is explained in The Conjuring 2 that Lorraine has a premonition of Ed being impaled.