Continuity mistake: Patty and Skinner go to see 'Space Mutants IV: The Land Down Under'. In a season one episode, 'The Telltale Head', a sign on the Springfield Aztec movie theater reads 'Space Mutants IV: The Trilogy Continues'.
Continuity mistake: When Mr. Bergstrom and Homer are eating together, Mr. Bergstrom's left hand is up and holding a fork, but the next shot shows his left hand resting on the table.
Continuity mistake: The long shot of Homer and Mr. Bergstrom eating lunch together at the childrarium shows Mr. Bergstrom's left hand resting on the table, but the next close-up shot of the duo shows Mr. Bergstrom's left hand up, holding a fork.
Continuity mistake: While Homer and Barney are smoking in the boys bathroom, when Principal Dondelinger walks in on them the "boys" sign on the exterior side of the door disappears in the closeup, but the sign reappears as Dondelinger exits. The door push plates on both sides of the swing door also vanish/reappear during the scene. (00:04:35)
Continuity mistake: After Lisa paces around the school hallway practising how to ask Mr. Bergstrom over for dinner, when she opens the classroom door there's a backplate behind the doorknob and a lower panel under the window, but when she sees Miss Hoover and gasps, the backplate and lower panel have both disappeared. (00:13:35)
Continuity mistake: When Miss Hoover returns to class she writes "psychosomatic" on the blackboard, but when Lisa runs out of class the word has vanished from the board. (00:13:55)
Continuity mistake: When Homer shows up to the Bouvier home the night of the prom, Selma and Patty open the door and it opens outward, but in the following shots the door has been opened inward. (00:16:10)
Continuity mistake: When Marge comes downstairs she's shocked to see Homer in her house, and when the doorbell rings we see Mrs. Bouvier wearing an orange belt with a red buckle, but then the colors switch to an orange buckle and the belt center is red. (00:16:45)
Continuity mistake: When Homer stands outside the Bouvier house to pick up Marge, the home's front door has three diagonal windows from upper left to lower right. However, when Marge gets home later after the prom, the three windows are diagonal the opposite way from upper right to lower left. (00:16:10 - 00:21:00)
Continuity mistake: When Martin tells Bart about the answers being worthless, Bart is stood by the grass or the kerb depending on the shot. (00:04:00)
Continuity mistake: When Bart gets off the bus there is a fire hydrant behind him. When we see the bus drive off the hydrant has gone. (00:07:10)
Continuity mistake: When Bart gets on the bus the day of the test, Milhouse is sitting at The Front of the bus. When we see Sherri and Terri looking at Bart, Milhouse has gone. (00:06:30)
Continuity mistake: When we see the big ape on the TV, the people running keep changing colour from black to white. (00:05:00)
Continuity mistake: When Homer puts Lisa's test on the fridge, a lot more papers appear on the fridge. (00:04:50)
Continuity mistake: When Mr Burns and Smithers are standing outside Springfield Stadium, Mr Burns says to Smithers, "Put a little smile on his card" and Smithers is writing it down with a pencil in his left hand. When the Simpsons arrive in the next shot, the pencil has changed into another piece of paper.
Continuity mistake: When Bart says to Homer that he's on "Jumbo-Vision", the man behind Homer is drinking from a paper cup with a straw, but when we see Homer on the screen, the paper cup has disappeared.
Continuity mistake: When Moe is wiping the beer glass at the beginning of the episode, the glass is initially smooth but changes to dimpled in the very next shot.
Continuity mistake: The door to Mrs. Krabappel's classroom has a window, but when Bart fakes being sick then walks out of the class (we see the desks as the door closes), the door's window has vanished, and the doorknob has switched sides as well. Additionally, earlier, when Bart deliberately falls off his chair in class, note that one of the bars on the back of his chair has gone missing. (00:07:35)
Continuity mistake: After Mrs. Krabappel asks Bart to name the pirate in Treasure Island, when it cuts to a closeup of Bart we see the set of blue books have vanished from Mrs. Krabappel's desk, and a Krusty mug has suddenly appeared there. (00:03:00)
Continuity mistake: When Bart fails the test despite having actually studied, we see the two red "X" marks in the center row of the multiple choice questions, but after Mrs. Krabappel passes Bart because he applied practical knowledge, when Homer hangs the test up on the fridge those two "X" marks in the center have vanished.
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.