Continuity mistake: In the close-up when she clutches Ghostface's mask, Casey's hand is significantly bloodier than in the rest of the scene and the sleeve that was creased down straightened itself, with a different bloodstain. (00:11:35)
Continuity mistake: When Casey pops up to peek at the window and is face to face with the killer, she shakes with fear reacting very naturally, but in its close-up her left arm is sticking out perfectly steady and firm in an incredibly unnatural position, blatantly there holding still just so the killer can grab it. (00:10:20)
Continuity mistake: When Casey peeks at the letter opener on top of the TV, her hair is on top of the cordless phone; in the shots from the side, before and after, her wig is pressed against her cheek and ear by the phone itself. (00:08:40)
Continuity mistake: There's a close-up of Drew Barrymore's foot when she unplugs the lights when the killer is starting his trivia. She tosses the cable and plug blindly behind her. In the next shot, the plug is closer to her foot and the shadow resulting from the change in light is also different. (00:06:25)
Continuity mistake: If you look at the close-up of Casey's hands when she locks the door, you can see her left arm in frame, but in the next shot she is holding the phone to her ear with it. Later on there's a mistake even more blatant as she unlocks momentarily the patio door to check on Steve; in close-up she uses her right hand, the killer reprimands her for the stupidity of the move, and she pulls back her left hand, as the right hand is once again the phone hand. (00:02:55 - 00:05:45)
Continuity mistake: At the police station, Billy looks back with anger at Sidney after the sheriff tells him that they have to detain him until the phone records come in. The sheriff is looking at him with his arms crossed, but in the close up on Skeet Ulrich the sheriff's got his hands on his thighs. (00:34:10)
Continuity mistake: When Sidney and Billy are talking in the bedroom at Stu's house, when the camera is on Billy, Sidney's hair is in a different position than when the camera is on her. (01:20:00)
Continuity mistake: At the end when Sidney is in Dewey's police car and the killer is there, she opens the door and falls out but the door is still locked. In some cars you can open the door when it is locked but the lock always pops up after you open the door, and this one didn't.
Continuity mistake: After Courtney Cox runs to the van when she's being chased, she hops into the van and throws it into reverse, guns it, then slams on the brakes, and the body falls down onto the windshield. Slamming on the brakes after going in reverse would cause the body to fall the other way, toward the back of the van. (01:22:50)
Continuity mistake: When Randy answers the phone he kneels down putting his head about level with the top of the TV, yet when Sidney goes to drop the TV on Stu's head the TV is much higher.
Continuity mistake: In the opening scene, Drew Barrymore put the Jiffy Pop on and it sizzled right away. In reality, it takes about ten minutes to heat up. And also she should have shaken it when it started sizzling. (00:01:25)
Continuity mistake: Sidney is on the roof trying to escape from the killer and she falls off. When she gets up she sees the dead body of Tatum in the cat door and her left arm must be behind her because you can't see it but this isn't what happened when you saw her die. Her left arm was inside the garage and was beside her. Unless if fell off, it should be next to her body.
Continuity mistake: When the cameraman is watching the 30 second delay footage and the ghost face is about to kill Randy who is on the sofa, he walks into the room in a different way on the delayed footage to on the actual film footage.
Continuity mistake: When the principal comes back into his office after checking out who was knocking on his door you can see a closet in the background with coats in it. When they change the angle the jackets have moved to a different position. (00:50:35)
Continuity mistake: When Drew Barrymore is running to the kitchen after the patio windows break she grabs a knife. When they show her going through the doors from the inside to go outside her knife's curving blade is pointing toward the celling but when the show her leaving the house through the doors from the outside the knife curve blade is pointing down. (00:09:25)
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.
Manky
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.
dewinela