What is the cockamouse in How I Met Your Mother? Craig Thomas reveals the creature was based on writer Courtney Lang's real-life incident

Josh Radnor and Craig Thomas recently discussed the creature cockamouse in the latest episode of the podcast, How We Made Your Mother, on May 5, 2025. Notably, the creature was first discovered at the apartment by Marshall Eriksen and Lily Aldrin in the seventh episode of How I Met Your Mother season 1, and it could fly.

Notably, Josh and Craig spoke about alien life when the former started addressing cockamouse, calling it a “mythical creature,” similar to a centaur or Satyr. The actor claimed it was possibly a combination of both, leading to the emergence of something “greater and weirder.”

Craig then opened up on how the idea of the creature was formed, as he was heard saying:

“This is based on a true story. Courtney Kang, one of our writers, she was already on the pod a few back for return of the shirt.”

Thomas further stated that although the creature featured in the CBS sitcom was inspired by a real-life incident involving Courtney, it ended up being in a script that was not originally written by Kang. Craig continued revealing more details about cockamouse and referred to Courtney by stating:

“She was living in New York for a summer. She’s not from New York but she lived there, I think, after college or during college, and she and a couple of roommates saw something that some of them thought was a rodent and some of them thought was a cockroach.”

The television writer said that Kang and her roommates had a debate after witnessing the creature since the incident reportedly happened during the 2000s when there were no cameras on mobile phones. Thomas further stated:

“There’s no proof. I hear the haters out there and the doubters, but it’s all real. Courtney swears this happened, and she and those friends, I think, spent years debating what was that. They decided it had, it really had characteristics of both. That part was real.”

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Cockamouse in How I Met Your Mother: First appearance and other details explained

As mentioned, the creature first appeared in season 1 episode 7, Matchmaker, and was first seen by Marshall Eriksen and Lily Aldrin. The duo immediately informed the rest of the group members, and at first, they refused to believe Marshall and Lily.

Marshall eventually caught the cockamouse in the trap and went to the Columbia Biology Department. Marshall spoke to a biologist at the institution, expecting that the latter might identify it. However, the creature was missing from the trap, and it appeared again at the apartment, following which Robin Scherbatsky believed that Lily and Marshall were not lying.

Marshall then tossed it out of the window, and although the group believed the cockamouse was dead, they discovered it could fly. The window was shut down before the creature could enter again inside the house.

The creature later scares Zoey Pierson in the episode The Perfect Cocktail when she spends time with Ted Mosby at the downtown Manhattan-based hotel The Arcadian. The creature lived at the hotel after coming out of the apartment and also had kids in the same place.

The cockamouse had the features of a mouse and cockroach and resembled a potato with antennae, an exoskeleton, fur, and whiskers. The creature had an attraction to cheese and seemingly believed to be of a dark color, considering that it was not properly seen.

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How I Met Your Mother aired for 208 episodes over nine seasons. The show ended in 2014 and featured popular faces in the lead, Cobie Smulders and Neil Patrick Harris.