Continuity mistake: When Otto is playing the guitar with bart in the middle of the night, there are close-ups of Otto whenever he is singing. You can see that the wall behind him is plain. However, when there is a wide shot of otto and bart, the wall behind otto has two tables leaned against them. (00:15:50)
Other mistake: Near the beginning of the episode when Selma and Sideshow Bob arrive at the Simpsons' house, Bart and Lisa scream and hide behind Marge. Selma says "What the - ?" but the DVD subtitles say that Marge says it. It is shown "MARGE: What the - ?". (00:02:30)
Continuity mistake: In the cafeteria scene where Milhouse shoots a spitball at Kearney, in the shot when Milhouse says, "We have order, but at what price," Milhouse, Lewis and the bullies all change positions at their tables. You may have to watch this part several times to understand it. (00:16:45)
Plot hole: When Marge is looking for inspiration for her novel, she looks at the boat painting in the TV room. On the frame, she reads it and says: "Scene from Moby Dick". Yet in "The Trouble With Trillions", Marge said that she painted it herself for Homer. So then why would she have to read the label to find out where it's from if she painted it?