Revealing mistake: When Carl is being dragged away by the demons, you can see the cable line that he's attached to. May be fixed on DVD.
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.
Revealing mistake: During the party scene, when Jacob starts hallucinating, you can see the stick that one of the fake birds is attached to.
Revealing mistake: Outside the courthouse, there is a sudden downpour and the rain is coming almost straight down. Cut to a close-up of Van Damme and the rain is suddenly heavier, coming in at much more of an angle, and it's noticeable that Van Damme is not even getting wet. Cut back to the scene where Amanda is walking away, the rain is now back to being more vertical, is lighter and this shot shows that Van Damme's hair has not been touched by a single drop of rain.
Revealing mistake: When young Norman Bates is spying through the peephole on his mother, who has brought home a man to the motel, we see him in the shower. Although the curtain is translucent, we can see he is wearing a black speedo.