You need to watch the movie up until the scene where Sidney is on the porch talking to the killer. The killer says something along the lines of "Do you wanna die just like your mother..." and Sidney runs back inside. Now watch as she locks the door with the regular lock, and also the chain lock. The door is very much locked. The killer then pops out of the closet and attacks her, knocking her on the floor. She kicks him, and then runs to the door to get out. She unlocks the bottom lock and pulls the door, but the chain lock is still on. She tries to unlock it but is unable to before the killer comes, so she runs upstairs. She locks her bedroom door, and calls 911 on the computer. Billy comes in through the window, and drops the cell phone and she freaks out and runs back downstairs. Notice, she just pulls the front door wide open without ever touching the chain lock. Dewey is there holding the Scream mask, but what ever happened to the lock. It seems to me that if the lock was in place when she ran upstairs, then it sure shouldn't be unhooked when she comes back downstairs. I thought this mess-up could have been avoided.