For obvious logistical reasons, creating crossovers between animated shows is a lot easier than in live-action, and there is a brilliant one that exists between Rick and Morty and the amazing Cartoon Network series Gravity Falls – and it’s truly something you won’t notice unless you are specifically looking for it.
It’s not Rick and Morty’s only callback to the Alex Hirsch-created show, as there are minor other ones sprinkled throughout the existing seasons, but it is the best one.
That episode first aired on April 7, 2014, and the gag was paid off months later on October 27, 2014, as there is a mid-credits bit in the Gravity Falls episode “Society of the Blind Eye” where a main character loses those three items in a portal he is building.
In Season 1’s “Close Rick-Counters Of The Rick Kind,” there is a scene where Rick and Morty escape a pursuing troop of Ricks by opening a series of portals, and those with eagle eyes will notice there is a brief moment where a notebook, a mug, and a pen fly out.