When Bobby escapes from the insane asylum and jumps over the fence the first shot shows that the fence has a line of barbed wire along the top. The next shot there is no barbed wire.
When the girls are having their boyfriends over, the power goes out, and no one resets the breakers. Before Tracy does finally reset the breakers, they are watching TV. Lights are also seen on before the breakers are reset.
Bobby grabs the knife from fireplace, but he wouldn't know it's there because he hid it under the brick.
However as the girls had just thrown it into the fireplace, he likely saw it when he went to remove it from under the brick.
However as the girls had just thrown it into the fireplace, he likely saw it when he went to remove it from under the brick.
Just after Linda has been stabbed and falls to the floor, you can see Linda moving slightly, even though she has just died.
When Bobby kills the guard and drags him, there is no blood trail left behind even though he supposedly painted the wall with the blood from the back of his head.
When Linda is hitting Bobby with the shovel you can clearly see that she is hitting the floor behind him.
When Craig is running through the house naked after Tracy has been killed, he's clearly wearing pants in some shots.
The doctor doesn't tell the employee the old Bobby's address which doesn't make sense, since that's the first place he would go to and remembers to mention this only near the end of the movie.
The girls would clearly see what happened at the bottom of the ladder and wouldn't try climbing down since Bobby is waiting for them.
Bobby simply leaps smashing through the window of the second floor making the previous scene where he is trying to climb the ladder to get to them in that same room pointless if he could have just done that in the first place.
The spare key is a vital plot point at the end of the movie, but at no point were they locked in at all. Bobby let himself in through the front door, and while they are shown unlocking and locking one door, the other is supposed to be still unlocked.
The employee working at the state mental hospital says he doesn't have a file on Bobby and that he has to call doctor in charge. However, later on, he is shown looking through a large file on the patient, with all of the information required by the police. The only thing added by the doctor is which previous address he might potentially go to.
The boom is clearly visible in the shot when the girls are walking to class early in the film, with the arm of the boom visible too.