Continuity mistake: When Homer is showing Carl and Lenny the large bottle of wine he has found in the wine cellar, you can see there is nothing on the shield on the label, but when see Homer holding the bottle a few seconds later, the shield has now two lines on it.
Continuity mistake: When we see Homer in the audience at the conference at the beginning of the episode, he is sitting between a lady with grey hair and a man with black hair. But when we see a wide view of the audience a little later on, he is now sitting between a man with brown hair and a bald-headed man.
Continuity mistake: When Principal Skinner and his mother are with Bart and his friends after the toilet prank, you can see Bart has Milhouse, Richard and Lewis are beside him. In one shot, Bart is on his own and the other three boys have gone, and in the next shot, they are back again.