The title of this article is a conjectural. Though the topic is found within The Simpsons universe, a proper name is not available.
The Alien couch gag is the fourth couch gag of Season 3.
An Alien is seen on the family couch. When he sees the family is coming, he pulls a string and jumps down a hatch. The family than sit normally, never noticing the alien, though they all stand together and jump backwards.