The tattoos on Sarah's back disappear and reappear throughout the course of the movie.
In the drug store, Caleb's necklace repeatedly disappears and reappears between shots.
While driving Sarah to his family's first settlement house, Caleb points out the Old Putnam Barn. While they are driving it is not raining, but during the shot of the barn it is raining pretty heavily (probably due to the weather during shooting). The next shot is back to normal with no rain.
When Caleb is in his bed his perspiration disappears in the next shot after he wakes up to the ghost.
In the last scene when Caleb raises his hand to mend the windscreen, just as the windscreen is mended near his raised hand, his hand rises again from the bottom displaying the 'millisecond' overlapping mistake of the film editor.
In one of the classroom scenes, the instructor states that of the first 12 amendments proposed to the US Constitution, 10 were "eventually" ratified. In fact, 11 have been ratified. The 27th Amendment (originally the 2nd proposed amendment) was ratified in 1992, more than 2 centuries after it was written.
At the beginning of the "running errands" scene, a group of people walks down a sidewalk under an American flag that is hung backwards. The stars should be away from the building.
The string on Steven Strait's harness is visible during the battle in the barn when Caleb and Chase are throwing farm equipment at each other.
When Caleb is driving, before he sees the graveling and has the accident, he is on the left side of the road. There was no one else shown on the road, so he wasn't passing anyone, which means there is no reason for him to be on the wrong side of the road BEFORE he was frightened by the image.
William Danvers III is credited as James Danvers.
When Caleb and Chase have their confrontation in the old barn it's pouring rain. Although the roof shows gaps in the wood there isn't one leak or drip and there is no indication there was any magic used to prevent this.
Chase tells Pogue and Caleb that he heard they were swimmers while the pair are playing foosball at Nicky's, but his mouth doesn't quite match up to the words, almost as if he's yelling it and then it was voiced over.
During the scene at Nicky's, Pogue tells Caleb that Reid and Tyler are there and Caleb responds with, "Great, that's trouble." But when he says that's trouble, his lips don't actually move.
The opening scenes of the movie showing the beach party show large cliffs on the edge of the ocean, which do not exist in Ipswich. The town has a couple hills but is mostly flat. The shoreline especially is characterized by wide sand beaches and marshland.
While trying to escape the police, Caleb suggests that they have some fun and cut across Marblehead. Marblehead is not only nearly 20 miles from Ipswich, but is also a very densely populated peninsula.
Before the dance, there is a shot with Caleb's mom and Reid (Toby Hemingway) is in the background. For a split second in the background, Reid bumps against the stuffed leopard and then awkwardly tries to adjust it.
When the doctor is talking about what is wrong with Kate, he says "It's like she was bitten by hundreds of insects, like spiders." Spiders aren't insects and a medical doctor should know that.