As the kids start vomiting, Mr. Prince says, "I TOLD you we should have served cake instead of oysters. Yet, when Bart runs into Edna for the first time, there are clearly cupcakes on the table by him.
When Principal Skinner hands the envelope to Bart to give to Mrs. Krabapple, the words 'personal' and 'confidential' are written in red ink. When Bart looks at the envelope, they are in black, then out in the hallway when he opens it, they are in red again.