Homer says that at Krusty Burger, he ordered the "Double Double" and they gave him the "Double Double Double Double". This is a reference to In and Out Burger's famous Double Double burgers, consisting of two patties and two slices of cheese. A "Double Double Double Double" can in fact be ordered, but is known as a 4x4 and is on the secret menu.
The trivia items below may give away important plot points.
Joe Mantegna and Mark Hamill later worked together again in the final two episodes of Criminal Minds (2005)'s eighth season. Hamill plays a serial killer nicknamed "the Replicator" who, to taunt David Rossi (played by Mantegna) and his team at the Behavioral Analysis Unit, copycats crimes they've already solved.