When the woman is killed in the opening scene, she is electrocuted because she touches the frayed electrical wire plugged in to the wall outlet. The scene then erroneously cuts to her dead in the bathtub. Her body should have been located on the floor of the bathroom, next to the wall outlet that killed her.
Sheriff Tupper receives an anonymous letter and when he reads it, the letter is a single sheet of paper, no lines, with smooth edges. When he reads the same letter he received in the sheriff's office, the letter is a lined piece of paper with hole punches and a frayed edge.
When Amos and Harry are investigating the electrical outlet in the bathroom, the camera pans too far, revealing the edge of the set wall in the lower-right corner of the screen.
When Jessica and Amos Tupper are in Beverly's basement and they hear Adam coming to the basement, Jessica turns off the light bulb and then grabs it to unscrew it and take it with her to hide behind the boxes. The light had been on for several minutes so the bulb would have been too hot for her to handle bare-handed immediately upon turning the light off.