When the African student arrives in wood shop, he is told he is late because it is already June. The principal's office has a calendar hanging dated as March, however.
When the girl is about to take the chicken out of the fridge, it is supposed to be a continuous shot, but it isn't because the cut can clearly be seen.
Paper clip was not in the same position in the shot before the killer picks it up.
When wife enters the room after the murders at the start of the movie, the dead girls is obviously not in the position as shown when husband sees her.
In the end credits, during the listing of "thanks" to companies who have provided products and services, Chambord Liqueurs is misspelled as "Chanbord"
During the parade, viewers see the Lamab High School marching band. However, the band's uniforms clearly say Pearland, a Houston-area high school.
The husband of the couple Julie is babysitting for at the start of the film tells his wife to hurry so they can get home in time for Dukes of Hazzard. However, a clock visible in the house when they arrive shows it is after 1:30 a.m., much later than the prime time hour that Dukes would have aired.
Students at football game talking about what will be happening next week at graduation; football games are in the fall and graduation is in spring. However, in the principal's speech in the second scene, he acknowledges that all the school's events are happening on one day (along with the prom, which needs to be at the end of the year) due to a cut in the school's budget.
When Toby is on the gurney with the corpse, the dead boy's eyes move. Later his arm moves.
Obvious, muscular, male arms when Toby reaches up out of the ground to strangle Hardy.
Obvious, muscular, barefoot stunt performer when Toby dives out the school window.
Smoke coming from apparent flatulence by Joan's boyfriend thus revealing the sound was made by a machine.
Bertha is seen breathing when Toby finds her body in the car.
When Toby enters a classroom following her session with Dr. Sigmund, a shot of the students is flipped, showing words and letters on clothing backwards.
In the opening scene when the phone begins to shake from the "ringing" of the "breather" calling, you can see someone's forehead that's moving the phone on the table in the bottom right-hand corner of the screen, black curly hair. (In the DVD version the shot is corrected so you cannot see the crewman.)
Cameraman shadows appear twice toward the end of the movie.