Most iconic television credit sequences build their reputations because of repetition. But for 22 years, the opening credits for The Simpsons have instead made a virtue of variation. With every episode comes not only a new storyline, but also a new "couch gag": as the Simpson family converge on their home in suburban Springfield, they are greeted each time with a new visual route to the sofa.
It might be conceptual: one celebrated couch gag showed the evolution of the Simpson patriarch, from a D'oh-ing amoeba, to dinosaur fodder, to Homer sapiens. It might be post-modern and referential: in season four, the family arrived home to find the Flintstones on the couch; in season 14, Homer, on waterskis, jumped over a shark, just like Fonzie did in Happy Days.
There have been Lego and claymation couch gags, and, as if to demonstrate the show's firm grasp of the zeitgeist, a couch gag iPhone app, which Homer used to assemble his family in season 21. Perhaps the most celebrated couch gag of all came in 2010, with season 22, when the programme-makers invited graffitti artist Banksy to create his own. The credits sequence began as normal, but with Banksy spray tags visible all over Springfield.
The climactic, couch-based scene was shown projected on to a screen in a Chinese underground sweatshop, overseen by 20th Century Fox (property of Rupert Murdoch), in which small children painstakingly dipped each new animation frame in radioactive chemicals, or manufactured merchandise by hand, with the help of abused pandas, chained unicorns and dead dolphins.
Now Matt Groening and his fellow Simpsons writers are asking for contributions again – not from a celebrated artist, but from fans. "Submit your written idea for a couch gag (100 words or fewer) to appear in the opening credits of The Simpsons," suggests a message on the Fox website (fox.com/thesimpsons/couchgag), "and if your idea is selected as the winner, we may actually animate it."
The winning contribution, Fox claims, may even be aired at the beginning of next season's finale in May 2013. Says Homer: "We are looking for a brilliant, original way to get my butt on a davenport."