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.
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.
Other mistake: When the two Americans are walking on the moors, their shadows are always in front of them, despite them having changed direction numerous times. Additionally, with the moon always being behind them, how are their faces being lit?
Visible crew/equipment: As Wes steps out of the shower and is drying his hair, you can just see the reflection of the camera man in the glass on the right side.
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: 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)
Continuity mistake: When Trent and Bree are having sex, the ceiling fan is on then off.
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)
Factual error: The aircraft used to fly to Shangri-La is a Bristol Beaufighter, a single seat long range fighter bomber. It was not a transport aircraft and could not carry passengers. Some variants of the Beaufighter were two seaters but none at all could be used as small airliners as they do here. It is not possible to simply reconfigure the aircraft as shown here - the centre of gravity, balance and trim would all be thrown out. The resulting jury-built aircraft would be uncontrollable in flight.
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)
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.
Other mistake: Max says that Michael is the "Man of the house" and won't come in until he's invited, which Michael sarcastically does, except Michael isn't the man of the house - its actually his grandfather who owns it.
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.
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.
Continuity mistake: When Sister Irene's habit is ripped at the back, you can see a bra strap on her left shoulder which disappears when she is seen at the front and when the camera is closer to her back (when she has the pentagram carved into her).
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.
Continuity mistake: When chasing Jamie in the woods, Mikey's headlights go from normal chevy headlights to off-road high beams.
Continuity mistake: When Amanda and Daniel entered the bathroom from 'Saw', Adam's body is shown with his right leg shackled. However, in 'Saw' and in Adam's death flashback in 'Saw III', his left leg is shackled. (01:14:10)
Other mistake: When everyone is looking for Bobby, Matthew Lillard says that it is no use shouting because the glass is 100% sound proof. Yet when he is trapped in the cage, he hears Maggie screaming directions for him to dodge the ghost - not sound proof at all then.