The Rat King returns, and wishes to mutate the populace of the world into rats.
- Blindfolded Vision: Splinter fights the Turtles while blindfolded in the beginning, and easily bests them. In the end, he uses this against the Rat King, whose power is to see through rats' eyes. After losing his seeing-eye rat, and unable to see through Splinter's blindfold, the Rat King fails quickly.
- Body Horror: The failed human test subject, who begs The Rat King to give him cheese.
- Disney Villain Death: Rat King after Splinter blinds him and gets him to fall into a pit in the Undercity. We visit his corpse there in Darkest Plight two years later after Splinter falls down there himself thanks to the Shredder.
- Family-Unfriendly Death: Irma at one point accidentally sends rats plummeting into a fan. This is for the most part on-screen.
- Foreshadowing: In the cold open, Irma says rats have a lot in common with people. She also vows to one day figure out where April and Casey are always running off to, implying she'll meet the turtles.
- Ironic Echo: The Rat King, once he's rendered blind, is left to the exact same treatment he gave Splinter, being taunted and beaten while trapped stuck in the dark. Some of the camera angles and character movements are even exactly the same.
- Killed Off for Real: This episode features the death of this continuity's version of the Rat King, who gets a Disney Villain Death. He would return in "Darkest Plight" in Season 4, but as a hallucination, and his corpse appears in that episode.
- Lethal Joke Character: Ice-Cream Kitty proves surprisingly effective at fighting off the Rat King and his minions.
- Mythology Gag: The first person the Rat King plans to mutate into a rat is Irma. He actually did mutate her into a rat in one episode of the '87 cartoon.
- Never Trust a Trailer: Almost all of the marketing focuses on Ice-Cream Kitty, a character who is more or less just a comical subplot in an episode where The Rat King appears.
- The Plague: Rat King's plan is to turn people into rats then have them infect others until all of humanity falls under his control.
- Rodents of Unusual Size: The Rat King uses mutagen to create giant rats to serve as his Giant Mooks.
- Shout-Out:
- The part where Mikey throws Ice Cream Kitty at The Rat King is one to Pokémon. The cooler it was being kept in is even red and white like a Poké Ball.
- Rat King naming one of his rats Aristotle may be an indirect reference to Willard, where the lead rat was named Socrates.
- Casey Jones attempts to disguise his real voice by talking like Christian Bale's Batman.
- The episode's title is a reference to Of Mice and Men.
- The rat extermination service billboard that appears in several scenes behind the Rat King is "Jonsey Kitty" Rat Exterminators. "Jonsey" is the name of the cat in Alien that Ripley risks her life to save before escaping.
- Theme Naming: The Rat King seems to have taken naming his rats after famous Greek/Roman people; his "eyes" are Aristotle, and the giant rat he rides upon is named Caligula.
