The Koekoeken (also known as Mrs. McMurtle) is a villain and a mythical creature in the second episode of Season 1, Cat Food. The Koekoeken is played by Margaret Jackman, while at the end of the episode she's portrayed by Katie Proctor.
Role in Cat Food
In Cat Food, Stu suspects something unusual about his neighbour across the road. He does some spying, and once he tells his mother, she does not believe him. The Koekoeken fools Stu's mother and she requests that she (the Koekoeken) looks after Stu while she is out. While this is happening, the Koekoeken reveals to Stu that he was right, and she lives as other people by stealing their bodies. Stu manages to defeat the Koekoeken at a game using a sneaky tactic, but the day after, it is revealed that the Koekoeken challenged Stu's sister, Kelly, to the same game, and because she lost, the Koekoeken is living in her body using the same tactic as Stu.
In the episode, Stu visits a website for information about the Koekoeken. Here is the information from the website:
THE ORIGINS OF THE LEGEND
The Koekoeken (parasite) is a creature that has appeared in oral tales and legends all over the world. Deriving from ancient myths and folkore, it is a clever beast that is capable of living a thousand years, by tricking unwitting victims to play for their lives. References to these creatures have been found throughout history in art and literature.
The Koekoeken is nice to Stu right to the very end. To start her plan to steal Stu's body, she has to be nice to him. She offers him treatments for his "illness" while slowly telling him her backstory.
Stu, however, doesn't like her from his suspicions from watching her house from his bedroom. He only agrees to the Koekoeken's challenge when he realizes he has no choice.
When Stu tricks the Koekoeken, at the end, she is enraged at Stu's trick and uses it against him to steal her sister's body. The episode ends as The Koekoeken nicely explains what she did to Kelly.
Koekoeken in Dutch means cuckoo, echoing its parasitic nature.