When Enid's art class shows their first works the one painting of the ocean with two mountains turns from a day scene to a night scene between cuts.
The amount of liquor in the bottle on top of Doug's car magically increases, and the bottle changes positions on the car several times.
When the art teacher, Roberta, is asking Enid to explain her Coon Chicken piece, she shifts from fumbling with her art book in the wide shot to having her arms spread away from the book in the close-up shot.
When Doug is buying the beef jerky, he takes it out of a jar on the counter, removing a yellow lid and placing it next to the jar. In the next shot, the lid is back on the jar.
When the girls are sitting in the '50s diner for the first time, a pizza on the table in front of Rebecca appears and disappears repeatedly between shots.
When Enid rips open the wrapper of the champagne/sparkling wine there is no metal wire around the cork. There is always a metal wire (because of the pressure that is inside the bottle).
When Enid pulls out a 33 from Seymour's record collection, he claims that he has a large 78 collection. He might, but what they're looking at are his 12" 33's.
The actor who plays the high school principal in the graduation scene also plays one of the customers in the porno shop. This was not intentional - Terry Zwigoff cast him as a porno shop customer forgetting that he also played the principal.
From the way that Rebecca hands Feldman the Wheelchair Guy his complimentary coffee, it's obvious that the cup is entirely empty.
When Enid visits to submit her college application, Roberta says "They are forcing me to give you a non-passing grade in the class." In the latter part when the camera faces Enid, the sound is "in the class" but Roberta's lips could be seen saying "forcing me".
In the scene where Enid surprises Seymour at Cook's Chicken, the boom is clearly visible in one angle, reflected in the window behind Seymour's head.
Enid accuses Seymour of wearing a girdle, which is a piece of old-fashioned women's clothing. Seymour was actually wearing an abdominal binder, a medical device which is used primarily for back support.