Pet cannot speak, and communicates through gestures and body language, or by using his eye to communicate thoughts and ideas. No one knows where Pet came from, or what he is, although the Heimertz Family Circus refer to his species as the ithune.
He enjoys modern technology, and Nod built him a small elevator within the tower mansion to get around quickly (this was replaced by an actual elevator in the Knightlorian). Pet also enjoys watching television, particularly Around the World with Professor Paul.
Pet was a victim of the twins' pranks for several years, having been weakened into a passive fur ball from decades of being without his food source; Balm. After Ellen and Edgar tracked Balm into the mansion, Pet began to consume it until he had the strength to take his revenge on them. Pet poisoned Ellen with his tears, which made her act as sweet as any other Nod's Limbsian. Edgar eventually captured Pet, and tried to get him to cry into Morella's mouth, which would make her seeds mature. Unfortunately, Morella ended up biting Pet, which left a seed in his fur that poisoned him.
When the circus came to town, Pet and the twins called a truce, and Pet began communicating to them through writing. The twins did their best to try and save Pet, and managed at last to trick all the townsfolk to dig out the caved in Balm spring below their house at the end of "Nod's Limbs". Thought the mansion ended up being destroyed, Pet was saved, and he moved into the former Knightlorian Hotel along with the twins, Nod, Heimertz, and Dahlia.
After that, Pet helped the Edgar and Ellen in all of their plans and pranks, and joined them on their quest to track down Stephanie and keep her from obtaining more Balm from other springs. During this adventure, it was revealed that each balm spring is guarded by an ithune, which meant Pet has several "cousins" he was unaware of. So far, Pet is the smallest of all ithunes recorded.
Pet is a mass of hair, sometimes depicted with a purple or blue hue to it. He has no determinable features except a single yellowish eyeball on the "top" of its fur. He does have the ability to hear and eat, though no ears or mouth are viable.
Pet's personality and health is like that he has by the end of "Nod's Limbs" and throughout the Nodessey series. He enjoys pulling pranks with the twins, and helps them with their schemes, even when that means he's dressed a giant fly to attract a monster-size spider, or posing as modern art.
There is no mention of the Balm in the series, and Pet seems able to consume other food, and even has a "meal time" according to Edgar in "Trickery Dickery Clock". His favorite show Around the World with Professor Paul is replaced by a telenovela called Amores Peligrosos.
Pet has a lot of dreamlike fantasy sequences, imaging himself in impossible situations, often saving an object of his affection from danger. He seems to have a romantic side in this series too, and falls in love with several objects, like a mop and a sponge.