Revealing mistake: When Bluto is watching the sorority girls have their pillow fight and he falls down with the ladder, you can see him land on a grass mat that is cut into the lawn. It's funny because you can see the grass push in.
Continuity mistake: During the classroom scene, Donald Sutherland writes the word "Satan" on the board. In the first shot, the "t" in Satan in directly over the crease on the chalkboard. In the next shot, it is clearly on one side of the crease.
Factual error: The car Flounder drives is a 1964 model, built beginning late in 1963, but the events of the movie take place in 1962.
Factual error: In the scene where Pinto buys/shoplifts food from the grocery store and meets the Mayor's daughter, the cash register has an LCD display. A little too futuristic for a flick set in '62.
Visible crew/equipment: In the scene just prior to the food fight, as John Belushi goes through the cafeteria line putting the food on his tray (which moves frequently), note the cameraman's feet in the mirror over the food following him.
Continuity mistake: When Bluto is looking through the window of the girls' bedroom, the shot from behind him shows his shoulders are just above the window sill. The shots from inside the room show him to be a lot higher than this.
Continuity mistake: In the scene where Otter and Boon are hitting golf balls near the ROTC drills, Otter puts down the golf bag he is carrying and draws a club. The camera moves to the ROTC trainees, and when it comes back to the golfers, the bag is back on Otter's shoulder and there is no club out of the bag.
Visible crew/equipment: Near the end of the movie during the parade riot and Bluto is trying to escape, he jumps up on top of a building. You can see one of the uniformed soldiers bending down to give him help up onto the awning.
Continuity mistake: In the scene where Otter is making out with Shelly from Dickinson college, in the back of the car she is clearly shown with her bra off, and it his hanging on her right arm by one strap. When the guys come running out of the club seconds later to make their escape, Shelly is shown jumping out of the car and diving through the window of the car parked next to it, but her bra is now on and hooked as if it hadn't been removed yet.
Continuity mistake: During the toga party, the mustard stain on Bloto's toga, disappears and reappears.
Revealing mistake: In the scene where the Mayor is giving his speech just before the parade begins, there is a man sitting in the bleachers behind him making bizarre faces and hilarious facial ticks in plain view of the camera.
Factual error: At Professor Jennings' place, the stoned Boon and Katy sing "Hey Paula." The song was only pressed in November 1962 and didn't break into the charts nationally until late December of that year, whereas the scene depicted takes place sometime in the autumn of the same year, before the song would've even been recorded.
Continuity mistake: In the classroom scene, Donald Sutherland takes a bite of the apple and a split second later in the next shot, he has nothing in his mouth.
Continuity mistake: Before the hearing, Katy and Boone are talking at the bottom (half) of a stairwell when Otter comes down with a briefcase in his right hand and he puts his left hand on Boone's shoulder. In the next shot the briefcase is now in his left hand with his right hand on Boone.
Continuity mistake: When Flounder and Larry arrive at the Omega house for the party, sunlight can be seen coming through the windows, although it was night when they arrive.
Factual error: After trying unsuccessfully to call Katie at the all-night cafe, Boone questions where she could be at six in the morning. The scene occurs during broad daylight. If the time were accurate, this could not be so, since it occurred in November.