Revealing mistake: After Hank shoots Lou's wife in the kitchen, the camera shows Jacob walking into the house, then Lou's body on the floor with a puddle of blood around his head. If you watch closely, you can see Lou's left eye twitch.
Continuity mistake: The house that the main characters live in is shown very early in the movie. We see the people looking out of a large window in an upstairs bedroom, which faces the front driveway. But that window doesn't even exist when they show the outside of the house.
Revealing mistake: As Jacob is changing the tire, there is a hint of sunlight out as he and Hank are talking. As Hank returns from the plane, it's snowing and grey outside, as you see Jacob club Dwight. As Hank finishes killing Dwight, it's still snowing, but when Hank and Jacob discuss that he wasn't completely being dead, it's back to having sunlight and no snow falling.
Continuity mistake: Near the end of the movie after the fake FBI agent shoots the sheriff, there is a scene where you see the sheriff's dog lying next to him. When the dead sheriff is shown again a few minutes later there is no sign of the dog or even dog footsteps in the snow. (00:09:00)