When Beverly goes to her childhood home, the closeup of the doorbell says "Marsh." However, in the next longer shot, it says "MARSH." Also, the red and white wire going into the bottom of the doorbell in the closeup become two white wires in the longer shot, and the position of all four wires, two on top and two on the bottom, change.
When Beverly flees from the Marsh house, a truck approaches her and the horn honks. However, the shots of the driver show he has both hands rock-solid on the wheel, which means he can't honk the horn.
When Mike opens the refrigerator and the balloons pour out, there are four cans of pop in the door. There are three clumped together toward the refrigerator and one separate on the outside. When the camera cuts to a shot of Stan's head inside the refrigerator, all four cans are clumped together.
When the wind blows through the library, it blows off most of the books on the top shelf. However, in the next shot they are back in place as the ones on the lower shelves blow off.
When Ben goes to Beverly's room to get her shawl, the cloth she picks up is white with blue flowers. However, when Beverly comes in and he gives it to her, it is purple and pink striped.
In the sewers, as the paper boat first approaches and then departs from the friends, the shadow of the steadicam following it can be seen on the brick wall to the right.
When Audra falls out of the web in It's lair, she is covered in webbing. However, when Bill sets her down all of the webbing instantly disappears.
In the movie the words "Beep beep, Richie" are often used. In the novel it is explained that this phrase is meant to get Richie to shut up.
When Bill's mother plays during the first flashback, her hands are clearly mis-synched with the music. Her right hand is in the air when the melody plays, and her left hand doesn't move.
When Bill looks at George's photo album, the piece of paper with the word "George" on it has a bend in the right corner when Bill looks at it. But when he sets it down in the next shot, the paper is entirely unbent.
When Ben greets the class, Richie is wearing a shirt with vertical stripes. But when Henry is sent to the principal's office, he walks by Richie who is now wearing a shirt with solid colors.
When Tom takes the bottle of champagne out of the refrigerator, he is holding it in his right hand. In the next shot the bottle instantly jumps to his left hand.
When Beverly walks out on Tom, she is only carrying a suitcase and a coat. However, when she comes out of the apartment, she has an additional bag over her shoulder that she didn't have when she left the apartment.
When the Loser's go to Eddie's house, he says that he wishes the summer would never end. However, in the next few scenes, the Losers are seen at school.