Continuity mistake: While Ricky is on his shooting spree, he manages to shoot at an oncoming car, causing it to to crash and roll over. As the car rights itself, the driver and the car seats are visible. The right rear passenger window is also fully intact. Just before the car explodes, the driver has disappeared, along with the car seats and the same rear side window is now completely missing.
Continuity mistake: When Ricky's shown sitting during his psychiatrist's interview the chair's only two or three feet away from the desk. A shot or two later and it's suddenly closer to the room's wall.
Continuity mistake: When the mother superior enters the kitchen to retrieve a knife to protect herself, there is a coffee mug on the bench in front of a white vase. When she turns around to exit the kitchen, the vase is visible, but there is now no coffee mug. Even at a different angle the mug should still be visible as well.
Continuity mistake: When Ricky and the mother superior are at the top of the stairs, in closeup Ricky raises the axe right up over his head ready to strike and he has one hand at the bottom of the handle and the other hand further up the handle. Cut to the next scene where the mother superior is ready to leap from her wheelchair, and Ricky is now suddenly backed into the corner. With no room for the axe to be behind him, his arms are no longer raised and his hands are now together, both at the bottom of the axe handle.
