Continuity mistake: At the start of the film, when John is in the airplane, the position of the white cloth on his seat headrest continues to change. (00:01:35)
Continuity mistake: At the start of the film on the plane, there is a woman sitting next to John Doe whose glasses go from being on her face, to then hanging down on straps around her neck, then back on her face between shots, just before she flies out the plane roof. (00:02:45)
Continuity mistake: When John wakes up in his room (which turns out to be falling through the sky) in the initial shots of him on the bed, the items (train models, books, etc.) on the bedside table continue to differ. (00:03:10)
Continuity mistake: John opens the window to find out the house is falling, and a large object goes flying through the window next to the bed, smashing out all the glass and all the wooden frames. Seconds later all the wooden frames are now repaired, however all the glass is still missing. (00:03:45)
Continuity mistake: When John walks up to the bus ticket booth, the booth's glass screen is covered in streaks of blood. During the differing shots from inside and outside the booth screen, the amount and position of these blood streaks keeps changing. (00:06:35)
Continuity mistake: When John goes flying off of the bus, into the "real" world, he hits a large, jagged, uneven rock. Later when he awakes the rock is very smooth and rounded, obviously a different one. (00:07:25 - 00:08:05)
Continuity mistake: When the doctor is talking to John Doe, you see her grabbing his arm. Also there is a man in a green shirt passing by them. Then it cuts and she grabs his arm again. The man in the green shirt is gone but now there is woman in black where the man should be. (00:19:25)
Continuity mistake: When John and Maggie are at the old school, there is a teacher talking to a class which isn't really there. The teacher stands by the left side of the blackboard, which has large crosses drawn on it, in rows. It cuts to a closeup and the crosses are now smaller and more scattered. (00:27:25)
Continuity mistake: When Freddy is controlling Spencer in the video game you see from Freddy's view that his legs are crossed on the table. When it cuts to in front of Freddy he has one foot only on the table. (00:42:25)
Continuity mistake: When Maggie gets out of the cellar you see her with nothing in her hair. Suddenly she has leaves in it. (00:42:50)
Continuity mistake: When Freddy is about to cut over the parachute you see him move the blade close to John's hand. When it cuts, Freddy's blade has moved further up. (00:50:10)
Continuity mistake: When John Doe is hit by the bus you see the stunt double holding onto the bus. In the next shot you see John Doe holding his hands to the front window of the bus.
Continuity mistake: When Freddy is standing above Carlos in his dream, he drops many pins from his hand. When it shows the pins falling, you see Carlos with his hands to his sides, but when it shows Carlos, his hands are over his ears and repeats several times.
Continuity mistake: In A Nightmare on Elm Street, Mrs. Thompson tells Nancy that a trail of gasoline went through the boiler room, out a door and set the entire place on fire. In this movie, a molotov cocktail is thrown through a window.
Continuity mistake: When Maggie stabs Freddy with the glove, in one shot she has her tied hair down over her jumper, but in the next shot it is above her jumper, and tied higher.
Answer: In the book version of the first three movies, he took a saying from his abusive foster father: "Children are useless." He made it "Children are better off dead." He also killed one trying to rob him and felt a rush of adrenaline from it that he didn't want to lose, so he got addicted to killing.
Rob245