Revealing mistake: When Millie is being carried away, her head remains completely upright as though under her own control. If she was dead her head would hang back.
Revealing mistake: Tommy picks up a chair and breaks it on a desk, but the chair breaks just before contact. (01:25:30)
Revealing mistake: Tortured by the demonic voices in his head, Michael King goes into a self-mutilating frenzy with a kitchen knife, except that he squeezes the handle of the bleeding-knife prop a bit too hard and it squirts fake blood horizontally across his chest.
Revealing mistake: When the newscaster was filming Clinton giving a statement, the timer on the camera stayed at 0:00. The red "Rec" button, which supposedly was on, also looked fake. (00:10:35)
Revealing mistake: It is obvious that the actor, Ellar Coltrane, is watching and waiting for the cue for "Mason" to start drinking from his can of beer at the pool hall. (02:03:44)
Revealing mistake: Tanner Boatwright was used as a leg double for Augustus. In the part of the sex scene where they shoot from the feet up, you can see that the amputated thigh is thinner and has a slightly different colored tone of leg hair than Ansel's actual leg. (01:05:25)
Revealing mistake: In the beginning of the storm, a trashcan is blown down the street, by the wind. Most of the leaves, lying in the road, are not moving though. (01:28:05)
Revealing mistake: Jim parts his hair on the left side. The stacks of his books on display in the hallway include a photo of him with his hair parted on the right side, but otherwise looking the same. Hair that is persistently parted on one side will not easily part on the other side and lay across the head in the same way. (The image was reversed). (00:25:20)
Revealing mistake: When Felix talks breaking the fourth wall about the mysterious, vicious "Roxy", he shows her twitter page. The latest tweet is dated Mar 10. Since the school at that moment still has to issue the report cards for the first semester, it seems a little too far ahead in time. (00:08:40)
Revealing mistake: Late on in the film; Arnie and the female officer kick in the door to one of his teams house. Unfortunately Arnie is in his 70s now and not as agile as he used to be, the door was open and simply pushed hard. Look at the door, it has no damage and neither does the frame. Also, the door barely opens past a hard push. As tactically trained operatives they would not have pushed the door if it was ajar either, they would have opened it slowly to avoid startling anyone inside and warning them.
Revealing mistake: JR is in the weapon container of the crazy dealer, who passes him some of his goods. JR ends up holding in his right arm a MP5K and an M4A1, which combined are about 5 kilos, but then he passes him an M60 Machine Gun, which weighs over 10 kilos and that the relatively diminutive protagonist just handles throughout the scene gripping it with his left hand and making no effort whatsoever. (00:25:20)