When Homer and Apu discover Jasper in the freezer, he is holding a note in his hand. Homer takes the note out of Jasper's hand and reads it aloud. In the next scene with Dr. Nick, Jasper is seen holding the note again. However, when Dr. Nick opens the freezer door, the note is gone again.
In Lisa's daydream, she is surrounded by kids and furniture when Ralph enters. In the next wide shot (when Wesley is using "momma's pryin' bar"), the room is almost empty and all the other kids have disappeared.
When the Flanders are looking at the "Offensive Baseball Cap", it is green and sitting in front of a blue cloth. Later, when Apu and Sanjay are cleaning up and talking to the Rich Texan, it is blue and sitting in front of a blue cloth. Seconds later, the blue cap is shown in front of a red cloth. When Jasper is standing beside the Moon Pies, the hat is back to being blue in front of a blue cloth.
The Simpson gene supposedly makes Simpson men dumb, however it hasn't affected Herb Simpson in Oh Brother, Where Art Thou? (1991)(#2.15), Brother, Can You Spare Two Dimes? (1992)(#3.24), or Changing of the Guardian (2013)(#24.11). However, he did let Homer design a car without having any idea of his ability to do so, as well as dismissing concerns expressed by his team about Homer, which could be him being affected by the gene.
On Chief Wiggum's copy of "Yertle the Turtle," the last word of the title is misspelled "Tertle." This could be intentional to make it look like "Yertle".
Grandpa Simpson says that the Simpson men start out smart and then get dumb, and shows papers by Bart with good grades. But in the episode "Lisa's Sax," Bart is shown to be dumb in kindergarten and has never done well in school.