The "couch gag" is a running visual joke near the end of the opening credits. The gag generally changes from episode to episode, and usually features the Simpson family's living room couch. A typical gag features the Simpson family running into the living room, only to find some abnormality with the couch, be it a bizarre and unexpected occupant, an odd placement of the couch, such as on the ceiling, or any number of other situations.
In the syndicated version for the episodes from seasons 1 to 5, the couch gag for the episode is usually replaced with the one from season five's "Rosebud" where The Simpsons find an exact double of themselves on the couch (though the syndicated versions of the later episodes retain their original couch gags).
The couch gag is frequently used to make the show longer or shorter, depending on the length of the episode itself. For example, longer couch gags have been used to fill time in shorter episodes, such as in "Lisa's First Word" and "The Front" and "Cape Feare". An extended couch gag was also seen in the first episode to use the new opening sequence, "Take My Life, Please", where the family chases their couch on a tour across the world. Another long couch gag was in the show's 500th episode "At Long Last Leave," showing a montage of previous couch gags.