As she does laundry in the basement, Doris's shirt changes from pale to bright yellow. The filmmakers couldn't match the color during re-shoots.
As Peter says, "Hurry up, the bus is leaving," he lowers his right arm to his side. In the subsequent shot, it's up in the air.
As Lt. McGiver exclaims, "Let's get over there," Sgt. Ruggin grabs the yellow notepad with his left hand. Cut to another angle and the notepad is in his right hand, and it's gone as he runs out the front door of the police station.
When Mason and Mrs. Engle are struggling to gain control of the pistol, several shots are fired. In the close ups, you can see that the hammer is forward. The pistol used is a model 1911 variant and will not fire unless the hammer is cocked to the rear.
The door to Mrs. Engel's bedroom is diagonal from the doorway to the attic. However, when the hallway is seen through the attic doorway, there's only an empty wall across the hall.
When Doris shouts "You asshole" at Peter, her mouth actually says: "You're crazy!"
The camera and cameraman are reflected off of the shiny squad car parked in front of the police station.