Character mistake: When they are surprised by Gale, Billy angrily says to Stu "Man, I thought she was dead." To which Stu replies "She looked dead, man. Still does." However, Stu didn't have time to check on Gale, since she crashed the vehicle moments before Sidney is attacked by a Ghostface that had to be Stu himself (since he does the quick clothes switch coming from the car).
Scream (1996)
1 character mistake
Directed by: Wes Craven
Starring: Drew Barrymore, Matthew Lillard, Courteney Cox, David Arquette, Neve Campbell, Jamie Kennedy, Rose McGowan, Skeet Ulrich, Roger Jackson, David Booth, Kevin Patrick Walls
Revealing mistake: As Drew Barrymore is running from the killer outside he stabs her. If you look closely it is very easy to tell it is a rubber knife, because you see it bend off of her. (00:10:20)
Principal Himbry: Damn little shits!
Janitor: What'd you call me?
Principal Himbry: Not you, Fred.
Trivia: The original title of the film was 'Scary Movie', the same title as its spoof.
Question: Why didn't Casey ring the police, after the call when she realied he was taunting and making threats?
Answer: Characters in horror movies are notorious for not doing the most obvious things. It's most likely that she was scared and not thinking straight at receiving numerous threatening phone calls, particularly when she is threatened after hanging up on the killer.
Also, when she told the caller that she was "two seconds away from calling the police", his response was that they'd never make it in time. She also knew he was nearby as he made comments that indicated he could see her. She didn't know it was someone that knew her. She's a teenager and scared, so her judgement was clouded. She reached a point where she believed her only chance was to get away from him by either fighting him or getting out and hiding somewhere outside.
Even in real life, people don't always think of something obvious when a situation is actually happening. I was a victim of armed robbery and almost died. No matter how much you read/hear about what to do in those situations, actually being in one is much different. It's easy for someone else to observe and say what a person should have done.
Answer: Landline phones like the one used in the movie cannot dial out a phone number while the line is active. Considering the killer is continuously calling her, she can't dial out on the phone line. This is referenced in the movie itself when her parents arrive home, attempt to dial 911, and can't due to the line still being active.