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 a new "couch gag": as the Simpson family converge on their home in suburban Springfield, they are greeted with a new visual route to the sofa.
One celebrated couch gag showed the evolution of the Simpson patriarch, from a D'oh-ing amoeba, to dinosaur fodder, to Homer sapiens.
Perhaps the most celebrated couch gag of all came in 2010, when graffiti artist Banksy was invited to create his own.
The climactic, couch-based scene was shown projected on to a screen in a Chinese underground sweatshop, overseen by 20th Century Fox, in which children painstakingly dipped each new animation frame in radioactive chemicals, or manufactured merchandise by hand, with the help of abused pandas 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, "and if your idea is selected as the winner, we may actually animate it."
The Simpsons 24th season
When: Starts 7.30pm Sunday