Deliberate mistake: In chapter 15 "Bad Service" as Kim drives away and almost hits the kids which are supposed to represent the "Burkittsville 7", count them. There are three girls and four boys. Rustin Parr kidnapped 8 kids; 4 boys and 4 girls. Kyle Brody survived so the Burkittsville 7 should be 4 girls and 3 boys.
Continuity mistake: At the end of the movie, Tristen wraps the rope around her neck several times, trapping her long hair between her neck and the rope. In the very next shot her hair is hanging loose on the outside of the rope. There was no time for her to pull her hair out, and even if there was, she was hardly in the right state of mind to worry about her hair being caught.
Continuity mistake: When the main characters wake up to their cameras and notes being trashed and are discussing what happened, Tristen is besides Jeff in a shot. At this time, Tristen has nearly no shredded paper on her left side and is holding a lot of papers and folders in her hand. Then Jeff says, "Those d*ckweeds. Who else could it have been?" Tristen then says, "They came back from Cauffin Rock and ripped us off," as she throws down the papers. Notice there's a lot more paper on her and a lot less paper in her hand now.