In the last episode of 2019, yet another familiar face (and voice) returned for Rick and Morty season 4. After a two-year hiatus, the hugely popular animated sitcom returned to Adult Swim back in November. As previously revealed in the official Rick and Morty season 4 trailer, the new run of episodes is split in two. The second half is expected to premiere sometime in 2020 and is being kept firmly under wraps. The first half was comprised of five episodes and saw Rick and Morty deal with everything from death crystals and dragons to rival heist crews and trespassers of Rick’s private toilet facilities.

Rick and Morty season 4, episode 5, “Rattlestar Ricklactica”, however, saw the titular mad scientist and his worrisome grandson tread new ground. For years, co-creators Justin Roiland and Dan Harmon insisted that they would never delve into time-travel. After Morty was bitten by and accidentally killed a snake, the Rick and Morty episode spiraled into a dramatic and hilarious send-up of numerous time-travel movies. Nothing was safe - with everything from the Terminator franchise and Back to the Future II receiving the parody treatment by the way of Snakes on a Plane. In the end, Rick was forced to break his own rule - utilizing time-travel in order to simultaneously unleash chaos and curtail it. Part of Rick’s plan saw him goad the snake society into drawing the attention of an Interdimensional Police Agency.

The plan ultimately worked, with agents intervening to correct the timeline. As a result, all of the snakes ultimately ate their own tails - as per the ouroboros symbol often used as a metaphor in time-travel stories - before disappearing. With balance restored, Rick and Morty were left to close the time-loop they had helped create before settling down to presumably enjoy Christmas. True Rick and Morty fans, however, will no doubt recognize the odd-looking, testicle-shaped creatures that made up the enforcement collective. They previously appeared in Rick and Morty season 2, episode 1, “A Rickle in Time”. After freezing time for a period of six months, the space-time continuum proved unstable and was thus divided into multiple realities based on various character’s indecision. As Rick, Morty, and Summer attempted to fix the problem, they were beset by the very same agency. Though the trio ultimately saved their world and defeated the agents, that episode’s post-credit scene revealed that they were still very much a presence in Rick’s established multiverse.

In Rick and Morty season 2, the agents were voiced by the comedic duo, Key & Peele. In the Rick and Morty season 4 episode, however, only Keegan Michael Key returned to reprise his role. Given Jordan Peele’s successful foray into writing and directing such films as Get Out and Us, it’s likely that he was simply too busy. After all, as well as hosting the new Twilight Zone reboot, Peele wrote the first episode of HBO’s upcoming Lovecraft Country and the highly-anticipated new Candyman sequel. In Peele’s place, the partner of Key’s leading agent was voiced by Eddie Pepitone.

Though one of the voices may have changed, their preferred methods remained exactly the same. In order to reset the timeline, Key and his partner ventured through time to visit an early ancestor of the snake society. Interrupting the caveman iteration, the duo proceeded to beat the snake senseless - as a warning to never mess with the natural order of things. This is an almost perfect reflection of the post-credit scene from Rick and Morty season 2. After being defeated by Rick, the pair similarly tried to track him down. Unfortunately, they encountered and accosted Albert Einstein instead - inadvertently spurring on his theory of relativity.

A number of characters have returned through Rick and Morty season 4. Most notably, Mr. Poopybutthole finally received a fully-fledged return at last. Whether or not they will return in the second batch of episodes is currently unknown. Given Harmon and Roiland’s comments that the remainder of Rick and Morty season 4 will go a little more serialized and lead directly into season 5, it’s certainly possible that they could factor in. And even if not, Rick and Morty have shown that past characters can always pop back up at any time.

More: When Rick & Morty Season 4 Returns (& What To Expect)