Scary MovieGoofs
Continuity
(at around 37 mins) When the piano falls down the staircase, it is straight, but later we see after the killer escapes from her house and Doofy is at the front door, behind Cindy the staircase is spiral.
(at around 15 mins) When the gang is in the car traveling around the curb in the "flashback," Greg stands up through the sunroof. When he climbs up to the sunroof his bottle of Jack Daniels is empty, in the next shot it is full.
(at around 18 mins) In the flashback, when Shorty is pulling up (car still moving, but nearing a stop) the inside of the car is clear (no smoke). As the car stops, the inside is completely filled with smoke.
Factual errors
(at around 57 mins) Shakespeare in Love (1998) jumps about half an hour and then jumps back about fifteen minutes in between shots in the movie theatre scene.
Incorrectly regarded as goofs
(at around 43 mins) The same girl walks by two or three times when Cindy and Bobby are talking in the cafeteria. Shorty even refers to this, making it clear to most viewers that it's a joke.
(at around 12 mins) Ray asks Greg if his yellow shirt makes him look gay. Then the camera cuts away; when it cuts back, Ray is wearing a black t-shirt instead of the yellow one he just had on because he put it on over the yellow one.
(at around 26 mins) Ray's jersey number on the field is 13; later in his room (at around 51 mins) it's 12. However, some high schools use different numbers on practice and game jerseys.
Revealing mistakes
(at around 19 mins) When they dump the body into the harbor, they take him out of the trunk set him down on the wharf. You can see the fisherman set his hand down to catch himself.
(at around 36 mins) Wire visible on piano rolling down stairs.
(at around 33 mins) While Cindy is taking a bath she shaves and the razor is drawn along her wet hair but does no damage to the hair, revealing there are no blades.
Miscellaneous
(at around 1h 7 mins) When Cindy and Bobby are having sex, the pillows on her bed disappear and reappear several times.
Audio/visual unsynchronised
(at around 31 mins) The judge's mouth does not move when saying "must be an original piece" about Buffy's dramatic reading in the beauty pageant.
When Cindy and the Sheriff realize Doofy is the killer, he runs out of his office and ask two officers if they've seen Doofy. When they reply they haven't, he then asks everybody if someone saw him. One cop says that Doofy ran outside but, no cops are seen moving their mouth when this was said.
Crew or equipment visible
A crew member is visible through window of Cindy's room during one of the first scenes when we are introduced to Bobby.