A rat appears inside the broken TV set in the very beginning of the opening sequence.
When Jake lies down in a pile of trash, a number of rats run up to him and start crawling all over him, which Jake does not seem to mind at all.
City of Thieves
There is a rat in the episode "City of Thieves" who has its cheese stolen.
Memory of a Memory
From Bad to Worse
Science is Princess Bubblegum's lab rat. It is trained to read her notes and gather ingredients for chemical formulas. Princess Bubblegum awards Science the Royal Medal for Heroic Bravery for creating the formula that reverses the Candy People's zombification.
Holly Jolly Secrets Part I
A giant rat is seen in "Mystery Dungeon," where it bursts through the floor of the destroyed kitchen after smelling Tree Trunks's pie. Lemongrab knocks it unconscious, angry at the fact the rat ate the pie.
Numerous rats appear in "Little Brother." They are ruled by the Rat King. Kent goes on a quest to defeat the Rat King and succeeds. In the final fight between Kent and the Rat King, Kent uses his sword to defeat/attack many rats. All of the rats live inside the roots of the Tree Fort.
A family of mice live in the walls of the Tree Fort in "Shh!"
The Squirrel from "The Duke" is a squirrel who hates Jake for not printing his letters in Jake's newspaper column. She attempts to get another letter to Jake by throwing it at his feet, but Jake walks away without noticing. She attacks Jake at the end of the episode. The same squirrel appears again in "Princess Potluck" where she shoots Jake with an arrow.
Squirrels appear in "Storytelling." They are sleeping in a hollow tree when Finn peeks in the hole to see if they are kissing. Finn's presence startles them so they run in a circle and bump heads, knocking each other out.
Up a Tree
The Squirrel from "Up a Tree" was a main character in the episode. He wishes he was a flying squirrel and escaped from the tree in the episode with Finn. He answers most questions with "Yes... and no." He made a quick cameo in "Jake Suit."
- Rats generally have gray or dark navy blue bodies with gray tails. In "Little Brother" their fur is white and they have pink tails.
- Mice have a similar appearance to rats, except that their ears are larger and they do not have protruding front-teeth.
- Squirrels are brown to red-brown and have bushy tails, curled at the end.