Mousetrap Comes From a Tale Where the Magistrate Picks the Rat

Netflix’s Mousetrap is called Deuljwi (들쥐, “field mouse”) in Korean, and its Korean tagline reads “If I can’t prove it, I become the fake.” Netflix’s English line is “Prove I’m real, or I’m the imposter.” Close, but the Korean says you become the gajja (가짜, “fake”), and I think that verb is the whole old folktale squeezed into one line.

The rat that became the master

The Encyclopedia of Korean Culture files the story under shapeshifting tales and notes it’s told all over the country, sometimes simply as “the real master and the fake master.” A rat spends a long time eating the finger- and toenail clippings its master throws away carelessly. Then it does dungap (둔갑, “changing form by sorcery”) and becomes him.

The whole family accepts the fake as the real one. In the end the county magistrate rules on it, and the real man is the one thrown out as the impostor. He wanders for a long time. On a helper’s advice, he comes home with a cat, the cat kills the fake, and the fake turns back into a rat.

When KBS introduced the Netflix series in August 2026, it described the tale as one viewers had probably heard at least once as kids. So a lot of the Korean audience comes in knowing that the rat in this story doesn’t beat anyone in a fight. It gets the magistrate’s ruling on its side.

Nails you got from your parents

It’s easy to take the nail clippings as a tidiness lesson for kids. The encyclopedia puts the taboo somewhere else. Hair and nails were things you’d received from your parents, so treating them carelessly went against filial piety. The entry also reads the tale as a warning that being careless with what’s yours can end in losing yourself.

The variants are kind of wonderful. In some, the rat becomes a young groom or a son. In others, the trouble starts because a man left his hat and clothes lying around, or because a daughter-in-law fed the rat. The entry adds that a similar story has long circulated in India.

Mousetrap hands the verdict to a phone

The way I read it, the show keeps the fake and swaps the magistrate for authentication. In the teaser, Moon-jae, a novelist who’s barely left home in years, tries to get into his mobile bank and fails the fingerprint check. Netflix’s English description adds that his passwords stop working and that he’s stripped of his money, his name, and any way to prove who he is.

The Korean press release has a detail I like even more. Because he’s lived in seclusion so long, even the people around him don’t recognize him. Nobody around him can vouch for him, which leaves his phone and his bank as the only judges.

Director Kim Hong-sun said at the August 20 press conference that the story may be more realistic than people think, since similar things happen and more people are living alone. The series runs 10 episodes, and Ryu Jun-yeol plays both Moon-jae and the man who took his life.

If I were watching with someone who didn’t grow up with the tale, the one thing I’d tell them before episode one is how the old version ends. Nobody in the house figures it out. The cat does.