When Schultz (the custodian/janitor) is talking to Dwight and Paula, Dwight is holding Paula's hand with his left hand. When he walks away, it's his right hand that he removes so he can NOW grasp her hand with his left hand.
The clothes that Paula and Dwight wear in the scene where Paula models for the art class are the same clothes they wear later in the film on the day when Mrs. Knocht is murdered, which takes place after the art teacher's murder. However, in scenes that take place during the day of the art teacher's death, Paula and Dwight wear outfits that are different from those in the modeling scene.
When Dwight chops the #2 door with the axe, he only chops away the bottom pane of glass and the bottom of the wooden frame. The top two panes, as well as almost all of the complete wooden frame are intact. A few seconds later when he runs away with Paula, all of the wooden frame is gone.
When Dwight Ingalls is speeding in his Mustang through neighborhoods he has to avoid a little boy on a big wheel that rides into the street. This creates a large amount of smoke from the Mustang's tires. When the camera angle changes, the smoke is gone.
After Colleen takes off her panties prior to leaving the locker room, Mr. Dante and some fans see under her skirt and affirm the fact that she is not wearing any underwear. However, a skin-tone g-string is visible as her skirt flies up.