When Enid and Rebecca are following the "Satanist" couple, we see them walking down a street with a storefront to their left and a crosswalk sign behind them. They turn a corner with the building on their right, but then we them walking down the street with the storefront once again on their left and crosswalk sign behind them.
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 cigarettes and malt liquor because he says he's working 16 hours, he only takes one average size bite out of one of the six sticks of beef jerky that he is also buying. When he turns around to tell the store owner that he would have to buy him dinner first, his mouth is now overflowing with beef jerky without him haven taken another bite.
When Enid surprises Seymour at Cook's Chicken and Dana walks in, Seymour spills his ice all over the table and proceeds to scoop it into his cup but when the scene changes the cup is sitting on the table and Seymour's arms aren't moving (the sound effects continue). Then the cup disappears in front of Seymour.
When Enid and Rebecca are at the diner and Enid is looking through the personal ads, reading them aloud, Rebecca is playing with sugar on the table. She forms shapes in them that change unnaturally every time the camera goes back to her
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.