<P> The men celebrate at Moe's Tavern, but relationships sour when Peter tries to introduce Homer to Pawtucket Patriot ale . The drink is revealed to be an imitation of Duff Beer with a new label . This results in Duff, represented by the Blue Haired Lawyer, filing a lawsuit against Pawtucket Brewery for patent infringement, with Peter forced to defend the brewery to save Quahog . Fred Flintstone is the judge who presides over the case . During the trial, similar characters from both shows interact with each other including both shows' versions of James Woods . Fred rules in favor of Duff Beer, but declares that both Pawtucket Patriot Ale and Duff Beer are imitations of his own favorite beer Bud Rock . </P> <P> The Griffins prepare to return to Quahog, where Peter faces the prospect of finding a new job . Lisa gives Meg her saxophone, but Peter throws it away, claiming there is no room for any more luggage . Stewie points out that he took revenge on not just Nelson, but all of Bart's enemies: Nelson, Jimbo Jones, Principal Skinner, Sideshow Bob, and (for the sake of making a scatological pun) Apu . Bart is sickened by Stewie's violent tendencies and ends their friendship . Homer tries to explain his actions, but Peter reacts angrily and the two fight (à la fighting between Peter and The Giant Chicken) through Springfield . The pair gain superpowers when they hit the Springfield Nuclear Power Plant, then end up in Kang and Kodos' spaceship, where they lose their powers before landing in Springfield Gorge . Peter and Homer stop fighting and admit their respect and admiration for each other while agreeing to stay away in the future . Returning home, the Griffins find that the heat from Peter's comic has died down and the Pawtucket Brewery is safe when Lois doubts that the inhabitants of Springfield will visit Quahog to enforce the ruling . Stewie tries to pretend he is over Bart, but goes to his room crying while writing "I will not think about Bart anymore" several times on a chalkboard . </P> <P> The idea of a crossover with The Simpsons was first suggested while the thirteenth season of Family Guy was being planned out . Executive producer Richard Appel received Family Guy creator Seth MacFarlane's approval and input after brainstorming ideas . Appel then asked for permission from Simpsons executive producers Matt Groening, James L. Brooks and Al Jean to use their characters . This was approved; Appel was previously a writer - producer on The Simpsons for four seasons, and retained his former colleagues' trust . Dan Castellaneta, Julie Kavner, Nancy Cartwright, Yeardley Smith and Hank Azaria guest star as their Simpsons characters, but Harry Shearer, the final main cast member of The Simpsons, was unavailable . Asked how he felt about the crossover, Shearer replied, "Matter and anti-matter ." </P> <P> Family Guy writers pitched several storylines for the crossover, including one in which the Griffins stay with Lenny and Carl and never meet the Simpsons, and another one in which their whole series is revealed to be a figment of Ralph Wiggum's imagination . When the final script was read to the show's staff, Appel expressed his concern about the length of the episode . MacFarlane said that Fox would be happy to make it an hour long . Supervising director Peter Shin, a former layout artist on The Simpsons, spent time adjusting the Griffins to the specifications of Springfield--changes included dimming the whites of their eyeballs so they would not look too bright--and animating the eight - minute fight between Peter and Homer . Appel said there are no plans to do a sequel to the episode, but stated that "by season 43 of The Simpsons and season 27 of Family Guy, someone who's looking at a blank board is going to say,' Well, the Griffins went to Springfield...what if the Simpsons went to Quahog?' And more heads will explode at Fox ." </P>

What episode of the simpsons is the family guy crossover