Character mistake: It's said in the movie a vice presidential candidate never gave a concession speech. Geraldine Ferraro did this in 1984.
Continuity mistake: When Sheriff Cooper writes "Karsson" and underlines it on the chalkboard, the way it is written changes between shots. In one particular shot, the line he underlined it with is suddenly rubbed out.
Character mistake: When Michael goes to the antique shop, the sign out front is spelled wrong; it reads "anitques."
Continuity mistake: The alarm clock chimes; Juno Temple reaches up with her left hand, putting it on the upper part of the pillow. Michael Angarano crawls over her to turn the alarm off, but she's napping with her hand by her chin, on the bottom corner of the pillow. (00:02:40)
Factual error: When the underground garage of the market is flooded, the car that Kyle and Heather are in does not flood. A car is not water tight like a submarine. Even though the water does not cover the top of the car, water would flood the entire car within minutes.
Continuity mistake: Tom walks into Anthony's memory. Anthony is sitting by the pool next to a table with two glasses of beer, which are 1/3rd empty. A few minutes later the memory is replayed, but this time both beer glasses are mostly full. (00:49:50 - 00:58:35)
Other mistake: Aladdin slices off one head of the monster in the tomb. The body spurts copious amounts of blood and the severed head even bounces on him repeatedly, but Aladdin's shirt is immaculate afterwards. (00:04:40)
Revealing mistake: In the opening scene, Johnny and Hickey sit in the front seat of a car. Views out the side windows blur, there is a gray background behind Johnny instead of the rear window, and when Hickey holds the cross toward the windshield, the "outside" is all grayish-white. At one point, there is light on Johnny's right forehead, cutting diagonally downward (too linear to be the sun), and another time, there is light behind Hickey on his headrest. (00:00:31 - 00:03:30)
Continuity mistake: In the car after Martin tells Hans about the throat slitting story, Billy and him get into an argument about the violence of the story. Billy says "It's going to be violent, it's about seven fucking psychopaths!" Martin then says "Hey!" But you can see in the back seat his mouth doesn't move for that. Then it cuts to a close up of Martin and his head is in a different position, facing Billy where he was looking out the window a moment before. (00:58:05)
Plot hole: The killer has been living in the (apparently big enough) crawlspace between walls and floors, for over a decade. There is no explanation (or rationale) given on how he moved the various objects inside every room, closed doors, fed when the house was not occupied, hid the various corpses and, silly detail, concealed his own BO and the stench of his own living quarters, which is something hinted at when they find out his hideout. It is explicitly said that he is agoraphobic and does not get out, ever.
Continuity mistake: When Luke grabs a beer from the mini bar in the hotel, there's a lot of beer foam in the top of the bottle. In the next shot, when Luke's sitting on the bed, the foam is gone without taking a first sip.
Continuity mistake: Dinner at Forestier's home, and Georges Duroy does not know which knife to use to eat. The asparagi in his plate are across the small pie in the wide shot, and in close-up they are arranged entirely on the side without his intervention. (00:08:20)
Revealing mistake: Right at the end of the film when Sam, Patrick and Charlie are driving through the tunnel, when Charlie begins to stand up on the back of the truck, look slightly beneath his flapping jacket and you can see the safety wires attached to him.
Continuity mistake: In the intro, the mother is playing with her kid; notice that when she grabs the gladiator puppet she is holding it with the index finger above the shoulder in the wider angle, below in the frontal close-up. (00:01:00)
Factual error: When Dave shoots Justin 8 times, he empties the magazine of his semi-auto handgun, but he continues pulling the trigger, and the gun clicks several times. Semi-auto handguns do not "click" when they are empty, because it's impossible to pull the trigger. Also, the slide of Dave's handgun does not lock in the open position when the magazine is empty, as it should.
Continuity mistake: George's son is disappointed because his dad missed the ball game and tells him that he should have been there. Meanwhile Denise Richards approaches the cooking pot with her spoon in her right hand and the plate in her left. Close-up on her telling Howie that dad was busy, and spoon and plate switched hands. (00:18:45)
Other mistake: The news anchor in the opening scene noticeably flubs her lines at one point.
Continuity mistake: In the middle of the film, the girl scouts and the leader are having a juice break and in walks the love interest (the father of one of the scouts). In the shot where the leader walks towards the love interest, the way she carries her glass of juice changes from the top to the side.
Other mistake: After the medical student leaves the unconscious co-pilot to one of the other passengers to watch while he goes to the bathroom, she notices his hands grow cold after a bit. It is only then they realise he has stopped breathing, and then get a defibrillator out and are successfully able to use it to revive him with CPR as well. However if he has stopped breathing for long enough that his hands have started to get cold, he would already be way too far gone to be able to be revived.
Continuity mistake: Alexandre Lagarde puts his fork into the plate of the attractive client, much to the scorn of her husband. The morsel in close-up and the one she actually puts in her mouth are different. (00:06:10)