There is something deeply unsettling about someone else taking your place.
Now imagine the fear you would feel when that someone looks exactly like you.
Netflix’s upcoming Korean thriller Mousetrap (Deuljwi, 들쥐) takes that fear and traces it back to an old Korean folktale with a wonderfully creepy premise:
If a rat eats your discarded fingernails, it can turn into you.
Not simply look like you. In the traditional story, the rat can take over your life so convincingly that your own family comes to believe that you are the impostor.
It sounds like the setup for a modern psychological thriller, but versions of this story have circulated in Korea for generations.
Mousetrap gives that old fear a very contemporary twist: what happens when the thing that no longer recognizes you is not your family, but your phone, your bank account and the digital systems that now seem so deeply intertwined with our identity?
The Korean Folktale Behind Mousetrap
Netflix describes Mousetrap as being inspired by the Korean folktale, “The rat that ate fingernails” (손톱 먹은 들쥐).
The story belongs to a broader group of Korean tales known as 쥐둔갑 설화, or rat-transformation tales. The Academy of Korean Studies also lists names such as “The Real Master and the False Master” for versions built around the struggle between an original person and the creature impersonating him. (encykorea.aks.ac.kr)
The premise of the story is simple.
A man carelessly throws away his fingernail or toenail clippings. A rat finds them and eats them and eventually transforms into the man.
Then it goes home.
The family accepts the transformed rat as the real owner of the house. When the actual man returns, nobody believes him. In one version recorded by the Academy of Korean Studies, even a magistrate sides with the impostor, and the real man is driven away from his own home.
The solution is absurdly simple as the story's premise itself.
The man returns home with a cat.
The cat attacks the false man, who is revealed to have been a rat all along. Only then does the real owner reclaim his home and identity.
As folktales go, it is surprisingly close to psychological horror: although the frightening part is not the mere transformation. It is the possibility that everyone whom you thought knew you best may mistakenly choose someone else over you.
Why Fingernails?
The fingernails are not just a randomly added detail.
The Academy of Korean Studies connects the story to an older idea that parts of the body—including hair, fingernails and toenails—were inherited from one's parents and therefore should not be treated carelessly. It interprets the tale partly through the traditional value of filial piety, but also as a warning about what can happen when people become careless about the things that belong to them.
Growing up in Korea, one often heard the childhood warning:
If you throw your fingernails away carelessly, a rat might eat them and become you.
It is the kind of story perfectly designed to capture a child's mind.
But there is also a darker idea underneath it. A tiny piece of your body—something you barely think about once you have clipped it off—still contains enough of you for something else to claim your identity.
Centuries later, that idea feels strangely familiar.
We now leave traces of ourselves everywhere as well.
The only difference is that they are now fingerprints, passwords, photographs, account information and other personal data that we disperse across the digital realm.
Mousetrap Turns the Folktale Into Digital Identity Theft
Through the teasers, it is difficult to ascertain whether Netflix will be presenting a supernatural rat wandering around modern Seoul.
We can, however, speculate how Mousetrap updates the part of the folktale that was frightening in the first place: the loss of the ability to prove who you are.
Ryu Jun-yeol plays Je Moon-jae, a reclusive novelist who writes under a pen name and seldom leaves his home.
One day, his carefully isolated and protected life begins to fall apart.
His fingerprint will not unlock his phone.
His passwords stop working.
His money is gone.
One by one, the systems connecting him to his own identity stop recognizing him.
Moon-jae discovers that a mysterious figure known as “The Rat” has stolen his name, his identity and his fortune. To get his life back, he has to find the person who has effectively taken his place.
This is where the adaptation becomes particularly clever.
The old folktale asks:
What happens when your own family believes the fake version of you?
Mousetrap asks:
What happens when your phone, your accounts and the systems that run your life believe the fake version instead?
In some ways, that is even more frightening for modern viewers in this increasingly digital age when so much of our lives is at stake and in the hands of technology that we know so little about.
Ryu Jun-yeol Remembered the Folktale From Childhood
For Korean viewers, this is not necessarily some obscure piece of folklore rediscovered for television.
At the series' August 20 press conference in Seoul, Ryu Jun-yeol shared how he remembered reading the story as a child and was drawn to the idea of reinterpreting something traditional for a global audience.
That detail says a lot about why Mousetrap may land differently with Korean audiences.
International viewers can watch it simply as an unusual identity thriller. But for Koreans who encountered some version of the story growing up, there is another layer underneath it—the lingering memory of a very peculiar childhood warning.
Don't leave your fingernails lying around.
Something might eat them.
And then it might assume your identity.
Ryu also takes on his first dual role in the series, playing both the real Je Moon-jae and the “Rat” who has stolen his life. He said one of the challenges was making the two characters distinct without exaggerating their differences, relying instead on subtle details such as their gaze, personality and tone of voice.
That casting turns the old folktale's central question into something viewers can literally see on screen: when two identical men stand in front of you, how do you decide which one is real?
From Korean Folklore to Webtoon to Netflix
Like many other series covered in this blog, the upcoming Netflix series is also based on a webtoon - the Kakao webtoon Deuljwi, which Netflix gives the English title Field Mouse. The webtoon itself uses the traditional “fingernail-eating rat” story as its motif.
Director Kim Hong-sun, whose previous work includes Dear Hongrang, Money Heist: Korea – Joint Economic Area, The Guest andVoice, said he was drawn to the original webtoon's cold, unsettling atmosphere. Screenwriter Lee Jae-gon then expanded that premise into a more dynamic chase narrative.
The series also stars Sul Kyung-gu as loan shark Noja and Lee Kyoo-hyung as detective Sun-yong. Netflix has confirmed that Mousetrap will premiere worldwide on August 28, 2026.
Why This Old Story Still Works
The supernatural logic of the folktale may belong to another bygone era.
The fear behind it does not.
Today, much of our identity exists somewhere outside our physical bodies.
A fingerprint unlocks a phone. A password opens a bank account. A photograph can verify an identity. Databases, devices and institutions constantly make decisions about whether we are who we say we are. (How many times have you run into a security wall claiming that you are not indeed you?)
The modern rat does not need to transform into you.
It only needs everything around you to believe that it is you.
That is what makes Mousetrap such a natural modern adaptation of this Korean folktale. A story once capable of frightening children into being more careful with their fingernail clippings has become a thriller built around one of the most contemporary anxieties imaginable:
How do you prove that you are yourself when everything around you says you aren't?
Mousetrap premieres on Netflix on August 28.
Now that you know about the Korean folktale behind the upcoming series, perhaps you may find that discarded fingernails (physical and digital) are more deserving of your attention.
