In the final scene, when the Simpsons arrive back at their house they drive straight past it and Grampa Simpson is not in the garden. In the next shot they are stopping outside their house and Grampa Simpson is standing in the garden.
Homer's cigar reads "Knoxville World's Fair 1983", but the World's Fair was in 1982.
When the Simpsons are leaving for Terror Lake, Marge says the agents at "the Bureau" thought of everything. The Witness Protection Program is administered by the US Marshals, not the FBI.
Lisa makes a direct reference to the FBI Light Opera Society, but it is possible for the US Marshals to have something created by another government agency.
Lisa makes a direct reference to the FBI Light Opera Society, but it is possible for the US Marshals to have something created by another government agency.
Bart tells Homer and Marge, "I saw Sideshow Bob, and he threatened to kill me!" But Bob didn't threaten to kill Bart during the encounter in question.
In singing the Bos'un's song from H.M.S. Pinafore, Sideshow Bob changes the line from "He is an Englishman" from "it's greatly to his credit" to "it's clearly to his credit".