Continuity mistake: Nick's shirt he gave to Carly is way too big on her when she first puts it on. In the next scene it fits like it's her own shirt.
Audio problem: In the beginning of the film, when Trudy offers her son more cereal, her mouth doesn't move as she speaks. (00:01:45)
Continuity mistake: When Paige walks out to Blake in his car he kisses her. When it cuts his hand is suddenly on her chin. (00:04:55)
Continuity mistake: When Paige is 'spiked' by Vincent, she falls onto her hands and knees and her hands are in fists. Yet after Vincent starts filming her they have changed.
Continuity mistake: When Carly wipes the dust off the mirror in the wax museum, the initial double hand swipe is repeated in the next shot. (00:38:00)
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.
Audio problem: Carly leaves the voice mail message for Paige and the whole scene with the truck gets on the voice mail. When Blake checks his phone after the music stops, the message isn't the same as earlier. (00:48:00 - 01:09:45)
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.
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: When Carly locks herself in the truck, the owner throws to the ground the box holding the fan belt and a few other things, right beside the driver's side of the truck. In the next exterior shot, there is nothing on the ground. (00:50:50)
Continuity mistake: When Nick is having the conversation about stealing the car, he has a lighter against a beer bottle. When it cuts the lighter is out, and nowhere near as close to the bottle as it was. (00:13:20)
Continuity mistake: When Carly is in the wax bedroom near the end of the film, she is fending off Vincent with a bat. She lays the bat on the wax bed while talking, and it leaves an imprint in the wax. When she runs on the bed to the other side, the imprint is gone.
Continuity mistake: When Carly is taken into the basement under the gas station, her kidnapper turns the radio on when they enter the room and he locks the door when he leaves, leaving the radio on. When Nick runs inside the gas station, the door is unlocked and the radio is off.
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). (01:11:20 - 01:11:50)
Continuity mistake: When Carly wipes the mirror and sees the person in the window, the area of wiped glass on the mirror alternates between two different versions. (00:36:30)
Continuity mistake: When Carly has fallen into the road kill pit, the amount of dirt on her hands keeps changing instantly. (00:20:50)
Continuity mistake: When Carly, Nick and Bo are walking up against Bo's house, Carly's hands change from being crossed behind her back to hanging down between the shots.
Continuity mistake: When the weird man gives Carly and Wade a ride, he steps out of the car to let them out. However, he does this twice in different shots. (00:26:30)
Factual error: Wax doesn't burn, even when exposed to flame. Wax also will not conduct heat. The ending shows the House of Wax melting and burning to the ground, as if the heat is spread throughout the house. In actuality, only the small hole near the fire will melt; the rest of the house would be unharmed.
Audio problem: When Vincent is trying to stab Paige in the warehouse, he slashes her foot and she falls down. As he's trying to stab her through the metal grate, she's screaming but her mouth is closed.
Answer: It is simply a contraption to keep Wade in place so he doesn't move and the wax can be applied. It's also used to keep the wax out of his eyes, ears, nose and mouth.