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)
Brother From the Same Planet - S4-E14
Continuity mistake: After Pepi and Tom walk off into the sunset together it cuts to Bart handing Homer another beer, and the picture behind the couch has brown sails over the boat, but next shot it's colored properly with white sails. (00:21:30)
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: While Homer is in Lisa's bedroom trying to make things right with her, there are three pictures taped to Lisa's mirror. After Homer tells her the music may help, in the next shot Homer walks over to stand behind Lisa. Those pictures taped to Lisa's mirror are weirdly behind Homer's reflection, as if the pictures are taped to the wall behind Homer. Three shots later, when Homer tells Lisa he can fix the dollhouse, his reflection is accurate in relation to those three pictures taped to the mirror. (00:19:20)
Continuity mistake: After Homer's emotional outburst about the lack of bananas, when it cuts to the exterior shot of the Lovejoy house the doorknob is on the right side of The Front door, but when Reverend Lovejoy kicks Bart out of his house, the doorknob is on the opposite side. Later, when Jessica twirls the baton, the doorknob is on the right side again. (00:08:00)
Continuity mistake: When Marge runs after Bart because he's hiding something under his jacket, Homer pulls out a gate to block Bart's entrance to the TV room. Three different gate styles are shown. (00:20:35)
Continuity mistake: When Lisa opens the classroom door (opposite the teacher's desk) and is shocked to see Miss Hoover has returned, note the door opens outward (into the hallway) and the doorknob is on the right side of the door. When Lisa runs out of the classroom, that door now opens inward and the doorknob is on the left side of the door. (00:13:40)
Continuity mistake: In some shots Otto's beaded bracelet vanishes and reappears, such as when he's on the school bus before the accident. Also, note a watch suddenly appears on his left wrist then it disappears, on the school bus. (00:11:05 - 00:15:15)
Continuity mistake: While Otto plays the guitar at 3:00 AM, the tuning keys on the guitar head are first facing down, then the guitar head flips and the tuning keys are facing up, between shots. (00:15:45)
Continuity mistake: When Homer is wearing underwear while banging on the bathroom door the doorknob is missing, but next shot it appears on the door, and the closet door hinge also vanishes. (00:18:25)
Continuity mistake: When Otto's guitar playing wakes Marge and Homer they go to the garage. Note the direction of the door when Homer opens it toward the right, but when Marge asks Bart what's going on, the door's open the opposite way toward the left. (00:15:55)
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 Ned stops to snap at Lisa he's already yelled at Marge and Bart. Yet in the background you can see Marge among the secondary characters.
Continuity mistake: When explaining RDRR, Ms. Mellon writes "y=r^3/3" on the board behind her. But after she asks, "Don't you get it, Bart?", the equation disappears from the board and she writes it again.
Mothers and Other Strangers - S33-E9
Continuity mistake: A teenage Homer and his father travel to Utah to look for Homer's fugitive mother, whom they find. This completely contradicts the episode Mother Simpson, where Homer didn't reconnect with his mom until he was in his late thirties, and was told all his life by his father that she was dead, even believing that the grave of Walt Whitman belonged to his mother.
Continuity mistake: In the scene at the United Nations, the Russian placard is just a placard. In the next shot, the placard is attached with a rod to rotate it at the push of a button.
Homer's Triple Bypass - S4-E11
Continuity mistake: When we first see Krusty start talking to Homer, from the rear shot you can see Krusty is missing his pale colour on his face. However, in every other shot, his pale complexion is there. (00:15:10)
Answer: Willy referred to an encounter he believed he had with actual aliens, while Wiggum thought he was referring to the arcade game.