Continuity mistake: Elisha Cuthbert is a foot shorter than Jared Padalecki, so they stacked blocks under her shoes to make her appear taller (as seen in one of the extras). However, in full body shots there is nothing under her feet and she's much shorter than those shots when you can't see her feet.
Deliberate mistake: Due to the thin tissue and blood supply to the lips, after Carly ripped the superglue from her lips she should have bled profusely, requiring steady pressure for a minimum of five minutes. However, that would have obviously slowed the tension of the movie too much.
Factual error: According to netstate.com the average monthly high in the state of Louisiana is 93.3 degrees F (34.05 degrees C) with summer months often exceeding 100 degrees F (37.77 degrees C), making it impossible for a functional multi-story wax structure to remain functional for any extended period of time, regardless of wax content.
Continuity mistake: After Vincent has stabbed Blake in the neck at the campsite, a terrified Paige runs for her life and tries to hide in a large dark building (the abandoned sugar mill). Whilst she is running through dark hallways, she passes through patches of moonlight and we see that her eyes are dry, and her face doesn't exactly show an expression of terror (Hilton's poor acting perhaps?). However, seconds later, she crouches down to hide and the lights are turned on, and we see that she is crying and tears are streamed across her face, yet she was not sobbing nor crying before she crouched down, merely screaming and panting. Immediately afterwards, when she is searching through a box of discarded cellphones, her face is once again dry and her eyes not red, and it remains dry throughout the rest of the scene, despite her not having wiped her face at all (including the scene of her face right before Vincent impales her: her mascara is completely untouched).
Continuity mistake: After having shot Bo with a stolen crossbow, Carly and Nick search the Sinclair house for help. When Carly comes across a drawer filled with newspaper clippings and childhood photographs of the Sinclair brothers, Bo and Vincent are seen on these photos as having very fair, almost light brown hair, and yet in the film, the adult brothers both have very dark black hair. It is possible that they could have dyed it in the past, but considering one is a deranged psychopathic killer and the other his simple-minded disfigured sidekick, this seems very unlikely (admittedly, hair color can grow darker over the years, but not the the extent of changing color completely, and the photos of Bo and Vincent show them around 5 or 6 years old, not toddlers).