Revealing mistake: At the end in the "Matrix" fight scene, the killer throws Cindy against the wall, which moves at the top. Watch the gap at the top of the wall. (01:11:00)
Continuity mistake: At the end of the Matrix scene he throws Cindy into the wall, look when she hits the wall there is no sign of hitting the wall, but when she is falling to the ground they is an imprint like an oval on the wall. (01:11:05)
Revealing mistake: When Cindy is thrown into the wall just before the Matrix style fight, the wall bends, showing it is made of rubber or foam to protect Anna Faris. (01:11:05)
Revealing mistake: During the scene when Cindy and the killer are fighting Matrix-style, Cindy kicks the killer, and he knocks down the book case so it falls over him. There is a vase with flowers on the book case - when it falls down the vase still remains on the book case, glued to it. (01:11:30)
Continuity mistake: In the scene where Cindy was fighting the killer Matrix style, she threw a brass ornament at the killer like a Frisbee and the killer dodged it, and the brass ornament should have gone out of the window by smashing through it. But the window was broken by the killer flying out of the window after Cindy kicked him/her. The brass ornament has mysteriously disappeared into thin air. (01:11:40)
Revealing mistake: When Cindy is dancing in the air after kicking the killer, she is very obviously a CGI. (01:12:10)
Continuity mistake: When Cindy has kicked the killer out of the window she runs over to her dad. His hands are supposed to be tied, but the ties are actually already loose. (01:12:35)
Continuity mistake: When Cindy is fighting the killer during the Matrix spoof, there is a short, storage table to the right of the plaid curtains. When the killer flies backwards through the window, that table is to the left of the curtains. (01:14:00)
Revealing mistake: When the killer throws Cindy against the wall, causing the painting to fall, the outlines of the knee pads she's wearing under her pants are visible, while she's in mid-air. (01:14:20)
Revealing mistake: When the killer is getting kicked into the glass cabinet you can see a string pulling the glass so it will break. (01:14:25)
Revealing mistake: In the snatch and run scene right at the end of the film, when the store owner gets his gun, you can see he doesn't fire it, there are just sound effects. You can easily notice this because the owner's hand doesn't move when he "fires".
Visible crew/equipment: After the garage door comes down on the garage victim, a hand can be seen from the outside pushing her boot off her foot as she's frantically kicking her feet.
Continuity mistake: After the killer throws Cindy at the wall and then breaks the long table, Cindy runs and stands in front of the round side table and lamp, which are right beside the wicker chair. However, when she levitates, that table and lamp are now beside the couch.
Continuity mistake: When Buffy comes up to Greg and he is banging his fist up against the locker and cussing, you see his report card in on hand and you can see the outlining of the subjects but there is no "DUMB-ASS" stamp on it, but in the close-up there is.
Continuity mistake: When Bobby spews out, ahem, "the white stuff," it is all over the ceiling, but when it cuts back to Cindy and Bobby, it's not on the ceiling anymore.
Revealing mistake: When Cindy walks in mid-air Matrix-style, she knocks the killer backwards. In the next close-up, as he falls on his back, the outline of the thick protective padding worn under his clothes is visible.
Continuity mistake: The living-room in Cindy's house has wood plank flooring, which is perpendicular to the plank flooring in the hallway, as seen at the doorway when she runs down the stairs and locks the front door. However, when she runs up the stairs as the killer chases her, the living-room wood flooring at that doorway is gone.
Deliberate mistake: When Cindy is talking to the killer on the phone, and he says, "I could be anywhere. I'm like the wind, baby," she walks into the living-room. Notice the wall behind the couch, it is completely different a moment later. When the killer hides behind the curtains, the wall behind the couch has large bay windows with seating underneath. Then when the killer is at her house the second time, all the windows are gone during the Matrix send-up, so Cindy can run along that wall.
Visible crew/equipment: During the Matrix send-up, after Cindy throws the platter at the killer, an actor's T-mark is visible on the floor, when he leans back and flounders about.
Continuity mistake: When Cindy and Bobby are talking in the school cafeteria after he gets out from jail, the students in the background keep disappearing as they go off camera from shot to shot when they should be seen walking away behind the characters.
Chosen answer: I know for sure they were making fun of the movie 'Usual Suspects' (dropping the cup) - they might have added the gag of the fish in it to appear as though she was shocked by the fish instead of the true identity of Doofy.