In the final scenes, the blood on Mia's face changes a number of times, not only the pattern, but it changes from dry blood to wet blood (which makes no sense because it is raining blood).
After Eric is stabbed in the eye several times and pulls out the needle from under his eye, in the following scene the mark from the needle is lower on his face than where he pulled the needle out from.
The double barrel shotgun keeps changing. It goes from having a pistol grip stock to a full stock.
After Mia deals with the last demon, she walks into the distance, limping on the wrong leg.
Mia loses the cap of the chainsaw, but it comes back on when she is underneath the pickup truck.
When Mia is underneath the pick up truck trying to work the chainsaw, she has cotton wool in her right ear.
The air nailer David and Natalie use doesn't have an air hose attached.
After Mia crashes the car into the pond, the car has its footwells full of water. The doors are above the water line and at such an angle that it could not flood as shown. The car's depth in the pond is also inconsistent with the area immediately around the car; Mia exits the car and into the water at a depth near her waist.
Near the end when Mia is about to kill the demon with the chainsaw she gets it started but in one shot the chain is not moving.
When Mia tries to escape in the station wagon there is the sound of tires squealing on asphalt when the car is on mud.
Mia's necklace is broken near the beginning of the film and is miraculously back together by the time she puts it on.
When David is burying Mia, she speaks with no impairment despite her tongue having been split lengthwise.
When Eric goes to check on Olivia, he walks into the room and looks toward the bathroom door. As you can see the door knob is on the right side of the door, but when he goes to open the door, Camera shot from the floor, the door knob is on the left.
In the beginning of the movie, Mia makes David cross his heart. He makes the motion over opposite side of his body (his right side).
When David is burying Mia, the book's position changes several times.
At the beginning of the film a woman is speaking a foreign language, according to the subtitles she is speaking Turkish, she is actually speaking in Welsh.
In the first half of the movie Mia severely scalds herself with boiling water leaving large blisters and burns on her face. These marks disappear without explanation in the film's finale.
When Mia leaves in Olivia's car, it has a Michigan plate on the front. Michigan does not issue front plates.