The couch gag on The Simpsons' latest Treehouse of Horror not only celebrated the show's newest episode milestone but also parodied Planet of the Apes and was offered up in virtual reality to Google Cardboard owners.

Say, what? 

For those of you who aren't fans of The Simpsons, here's the deal: Treehouse of Horror is the name of The Simpsons' Halloween specials. There have been 27 installments, with the latest being Treehouse of Horror XXVII, which aired 16 October. It was the 600th episode of the animated Fox comedy, and it broke new ground by embracing virtual reality, with the help of Google Cardboard.

At the end of every opening sequence, The Simpsons features a running visual joke called a couch gag. Sunday night's couch gag was offered in VR. Got it? OK. So, the opening of Treehouse of Horror XXVII was a Planet of the Apes parody called Planet of the Couches. Viewers could - and still can - download the Google Spotlight Stories app for iOS or Android to experience the couch gag in 360.

The 2D version of Planet of the Couches ran for 45 seconds and showed a landing page with a URL that directed fans to the VR edition, which includes an extra two minutes of bonus content. If you don't have a Cardboard-certified viewer, you can still experience the fun by turning your phones in different directions. There are six scenes you can enjoy, though physically turning your phone won't be as immersive.

However, according to EW, the first 25,000 fans who sign up at will receive a free Simpson Cardboard viewer.