Revealing mistake: When the scientists inject the mouse with poison, they put it in a jar. The, after they place it down you can see someone's hand swap the jar for one containing a dead mouse. You can even hear it. (01:17:58)
Continuity mistake: Just before the giant tarantula attacks the house where heroine Mara Corday is studying, you can see several book on the library table at the big picture window. The largest book on the table keeps shifting positions in several scenes.
Continuity mistake: When Trent and Bree are having sex, the ceiling fan is on then off.
Visible crew/equipment: In the second scene where the main character approaches the car, there's the filming crew visible in the right corner of the car's bumper. (00:02:30)
Revealing mistake: When the killer is attacking Cici on the balcony, you can see blood on Cici's back before she is even stabbed and both times she is stabbed, the knife that comes out of her back has no blood on it. (00:33:20)
Visible crew/equipment: During the beginning of the film whilst Tara is walking through the house, in the window to the right of the front door the camera guy can be seen during both scenes that take place during the hallway shots.
Continuity mistake: When Amber and Jonesy get an arrow through the head, the cannibal was on Jonesy's side, so the tip should have gone through Amber's head, not Jonesy's.
Continuity mistake: When Fin stops near the school bus, the bus number changes from "278146" to "278245" during the rescue of the kids.
Factual error: In the cemetery, the skeleton of Gregory Peck's son is far too big to be that of a newborn, which it is supposed to be.
Revealing mistake: When the man pushes Leroy's body down the basement stairs, as his body is sliding down, when it's almost to the bottom, you can plainly see Leroy lift his head up as he's sliding, although he's dead.
Revealing mistake: As the Predator tends to his wounded leg, one of his claws can be seen bending as if made of rubber.
Revealing mistake: When Bert is running in the woods, away from the local guys, he rubs blood on a tree to make them believe he ran a certain way. Look close, the tree already has red tint on it probably from previous takes that didn't wash off. (01:04:35)
Revealing mistake: When Louis is trying to get Gage off him near the end of the movie, as he's struggling in a few shots you can plainly see it's not really Gage but a dummy made to look like him. Looks like a doll. (01:33:35)
Factual error: At the end when Ben Willis and his son have Julie at the graves, Ray shows up with a gun. He fires at Ben but there is no bullet in the chamber. Later after the fight between Ray and Ben's son Julie picks up the six-shot gun and fires 8 shots at Ben.
Revealing mistake: In the library scene when Richie sees Pennywise the clown, all the balloons filled with blood are popping on people who aren't supposed to be able to see them, but one lands on a lady and you can see her jump as the balloon pops.
Continuity mistake: A blond boy in a light brown shirt is attacked by a crow and goes from having no blood on his neck to having a lot of blood smeared on his neck between shots. (01:14:10)
Continuity mistake: When the car door is ripped off by the cow, it shows the truck with the door intact.
Continuity mistake: In the scene where the Nemesis kills the 13 S.T.A.R.S members, after it blows up the sniper on the roof an additional S.T.A.R.S member can be seen outside the building on the right who wasn't there earlier. He then disappears shortly afterwards.
Other mistake: When Lawrence is looking at his wound in the mirror, it has slightly healed. Later, when Sir John visits Lawrence in the asylum, he shows the bite mark he got from the feral child to Lawrence. Since Sir John is also a werewolf, the bite mark should not be there.