This is the second time that a character discovers having a blemish and upon telling it "Not on my day you don't!" it instantly recedes/recovers (in this case, Homer being hit with a falling flower pot and receiving a bruised bump on his head). The first is when Marge discovered that she had a zit on her lip while preparing for her "third" remarriage (actually second, as Reverend Lovejoy's remarrying Marge and Homer didn't count as his ministering license had expired during that time) in the episode Wedding for Disaster.
This is the second episode where a Simpson rides on a garbage barge. The first being Homer the Heretic.
Despite taking place in September, the calendar in Ms. Krabappel's reads April. However, due to Edna's lack of interest in her job this is common for her to neglect her calendar. This goof also occurs in "Lard of the Dance."
When Skinner and the kids watch that a thief steals the bus parts, Otto is on the disambled bus. But in the next shot, he is among the kids.
When Maggie's toy cannon launches the knife, Mr. Burns doesn't have a scratch when the knife lands on him.