Continuity mistake: During the parade, Flounder dumps the bucket of marbles towards the camera, and they are all clear glass marbles. When the ROTC members slip and fall on them, the marbles are red, blue and yellow. (01:38:25)
Continuity mistake: When Pinto and Flounder attend the Omega rush party, a tasteful piano piece is playing. Niedermayer catches the eye of the brother at the piano, who smiles back over the keyboard. Soon thereafter, Niedermayer points out two important Omega brothers, who are standing in conversation across the room: Terry Auerbach, captain of the swim team, and Carl Phillips, editor of the Daily Faberian. The music has not stopped, but, when Carl turns to the camera, we see that he's the same guy who's supposed to be playing the piano. (00:03:15 - 00:04:55)
Revealing mistake: On the day the house is being emptied, after Bluto finishes the Jack Daniel's and tosses the bottle, there are no Jack Daniel's labels on it. (01:07:35)
Visible crew/equipment: During the scene where Otter is hitting golf balls at the ROTC cadets, Niedermayer is wearing a highly polished chrome helmet. In at least one shot, you can see a movie light reflected in it. (00:20:10)
Continuity mistake: When they show Flounder's face on the screen they throw beer cans at it and it gets soaked. When Otter gets up it is completely dry. (00:13:55)
Revealing mistake: When the people from the grandstand are flying up in the air after the Deathmobile hits it, you can tell they used a trampoline to get the effect as the woman are in their stocking feet; it would have been a safety issue if they jumped in high heels.
Continuity mistake: When Neidermeyer is yelling at Flounder about his pledge pin, Neidermeyer is spitting the P's in Flounder's face. When this happens, the camera is on Neidermeyer and if you look at Flounder, (even though it's his backside), you can see his eyes close everytime he's spitted on. However, afterwards, the camera changes to Flounder instantly, and his eyes are wide open (as if they never closed at all). Nobody's eyes instantly open THAT quickly after being spat on.
Audio problem: When D-Day, Bluto and Flounder are running out of Wormer's office after the horse died, there is a sound effect of them screaming as they flee the scene. This exact same sound effect is used when the boys run out of the all-black bar, except Bluto and D-Day weren't there; it was Flounder, Kroger and Boon. (00:30:40 - 01:17:15)
Continuity mistake: When the Deltas are leaving the student court on masse, you can see Bluto followed by Flounder exiting the hall as Vernon shouts "I'm calling your national office." After several more seconds of Vernon shouting and Greg frantically slamming his gavel, it cuts to a shot of the doorway with Bluto and Flounder just walking up to it and stopping to grin at Vernon. They would've been long out of the room by then.
Audio problem: At the bar after the tall black man asks to dance with the boys' dates, he lifts the booth table up off the floor. There's a sound like it's being forcibly ripped out of the floor, yet the table has a round bottom with no visible bolts or screws. While it may have been heavy, it wasn't secured to the floor.
Continuity mistake: As Niedermeyer chews out Flounder in the close ups, the long shots from Boon and Stratton's view of the action shows Niedermeyer mounted on his horse, then back to the close up of Niedermeyer dismounted, continuing to chew out Flounder.
Revealing mistake: You can see that the Jack Daniels that Bluto chugs is not real, because it foams. It was probably iced tea or something. (01:07:30)
Continuity mistake: From Double Secret Probation DVD - "When Bluto is placing the ladder outside the sorority house, there is a large awning between the two windows and it would be impossible for him to "jump" the ladder from one window to the next." (00:38:29)
Continuity mistake: In the cafeteria "I'm a zit" scene, Bluto picks up the mashed potatoes with his right hand, but the very next shot shows him placing it in his mouth with his left hand. (00:34:50)
Audio problem: When Bluto is using the ladder to look in the sorority house, the ladder gives a clanging sound like an aluminum extension ladder. The ladder Bluto is using is a single frame wooden ladder which wouldn't make any clanging sounds at all.
Continuity mistake: When Pinto and Flounder visit the Omega house in the opening of the movie, notice the girls coming down the stairs. In the first shot they are there, the second shot they are not, then they are. (00:03:00)
Factual error: Listen to the crickets chirping at the football field where Larry and the Mayor's daughter make love. It's fall, everyone has jackets on. It's much too cold for crickets to chirp that rapidly. (Or at all at that time of year). (01:32:00)
Continuity mistake: After Stork pushes the drum major off camera to the right and seizes his baton, the scene cuts to a longer shot where he leads the band in the same direction. The drum major has disappeared. (01:36:30)
Revealing mistake: During the scene where the Delta boys are looking at slides of the recruits from the evening, Otter steps in front of the screen to defend Flounder. Notice that he is standing directly in line with the projector to the screen and there is no shadow on the screen nor is part of the slide projected onto his chest. (00:14:10)
Continuity mistake: When the Deathmobile lines up across the street to take out the grandstand, the car reaches the grandstand about three times before it actually rams it. Even after one shot if the car reaching the grandstand, it cuts to D-Day yelling "Ramming Speed!" and then the car is seen back at its original position on the other side of the street.
Answer: Sometimes these things get left in because it's simply the best take. (The child covering his ears before the gunshot in "North by Northwest," for example.) It could also be that John Landis cast the extra because he wanted someone with goofy expressions in the crowd. He simply could have told the extras "Ok, be excited that you're at a parade," and that's how this extra did it.
Captain Defenestrator