The Simpsons have been known for their various couch gags in the opening credits over the years, but this is by far one of their most elaborate yet.

Made by Seth Green's Robot Chicken, it see Homer realising their boat picture is missing on the wall, and following Bart's suggestion that another cartoon stole it, he proceeds to jump into a world that is clearly supposed to be South Park.

"Is this a TV show, or did I walk into a third-grade shoebox diorama?" he says.

Ouch.

No doubt Trey Parker and Matt Stone will come up with a way to hit back at them soon.

Watch the full opening credits below: