One of the reasons that Rick and Morty is such a popular show is because of its spot-on pop culture riffs. After all, the two main characters were inspired by Back to the Future's Doc and Marty. So far, the series has parodied such genre properties like The Purge ("Look Who's Purging Now"), Mad Max ("Rickmancing the Stone"), and the inside of David Cronenberg's head ("Rick Potion #9").
Some references are more obvious than others, but one from the fan-favorite Season 3 episode of "Pickle Rick" has eluded discovery until now. It involves the post-credits scene, where Rick and Morty find themselves tied up and at the mercy of Concerto (Ryan Ridley), an insane music-centric villain that plans to bash their heads in with the hammers of a giant piano, which are controlled by a much smaller piano from on high. Before he can complete his "greatest performance of all time," his throat is slit by Jaguar (Danny Trejo), a deadly freedom fighter that Rick befriended and freed whilst in pickle form earlier in the episode. Killing Concerto is Jaugar's way of paying Rick back.
It could have stopped there without the due diligence of Reddit user Capgunkid, who noticed that the scene bore a striking resemblance to one from a 1998 episode of The New Batman Adventures, the follow-up series to Batman: The Animated Series. In "Legends of the Dark Knight" (itself a nod to the The New Adventures of Batman in the '70s) Batman and Robin are also tied up on a piano being played by the Joker, his wide, unnerving grin almost certainly the inspiration for Concerto's piano-keyed mouth.
Watch them one-after-the-other below and behold this one incredibly obscure Easter egg!
But wait, there's more! Jaazeps commented on the original Reddit post to point out that the animated Batman piano scene is itself an homage to the 1960s Batman TV show with Adam West and Burt Ward. The 1966 episode in question is titled "Dead Ringers" and guest-starred the famous pianist Liberace as the villain Chandell.
Our heroes are tied to a conveyer belt that leads to a machine that makes sheet music for player pianos. Chandell controls the machine with his "master piano," but Batman and the Boy Wonder are able to escape, simply by "outshouting the piano" with very specific notes.
Watch the sequence below: