13 timestamped notes explaining the Korean cultural context in this episode — customs, idioms, food, honorifics, and history, at the moment each appears on screen. These notes discuss events across the whole episode. To see them revealed scene-by-scene as you watch, use the episode page to find an airing.
The phrase 눈에는 눈 이에는 이 ("an eye for an eye, a tooth for a tooth") comes from the Old Testament and is deeply embedded in Korean as the go-to expression for the principle of equal retribution. Koreans use it the way English speakers say "what goes around comes around," but with a sharper, more personal edge — you give back exactly what was done to you, no more, no less.
Killing a goldfish (금붕어) or a pet named 초코 (Choco) is the kind of detail Korean true-crime culture treats as a classic early warning sign. School counsellors, police, and drama audiences alike read childhood animal cruelty as a red flag for violent tendencies — it is a well-known step in the local shorthand for a developing predatory personality.
Korean expressways use a card-or-cash 톨게이트 (tollgate) system, and the paper receipt stamps the exact time and location. Finding a receipt inside a pocket is genuinely useful physical evidence in Korean investigations — and everyday drama — because it proves someone was at a specific road exit on a specific date, in a country where highway travel almost always passes through a toll.
서번트 증후군 is the Korean term for savant syndrome, the condition where a person with a developmental disability has an extraordinary memory or skill in one area. The detail that Jae-hee could remember everything she heard once is exactly how Korean dramas — and Korean medical popular culture — typically describe the condition to a general audience.
Every South Korean citizen has a 주민등록번호 (resident registration number), a 13-digit ID tied to birth, taxes, school, and healthcare. 말소 (cancellation) means the number has been officially struck from the register — something that happens when a person is declared dead or emigrates. Having your number 말소 while you are still alive is essentially being erased from the country's identity system.
The drama has been building around a fictional prenatal test that claims to detect a predisposition to psychopathy (사이코패스) in an unborn child. While no such test exists in reality, the storyline echoes genuine South Korean public anxiety about genetics and moral destiny that peaked in popular culture debates around the 2010s, partly fuelled by high-profile serial-killer trials.
The detective is mocking the rookie with a crude body-based insult meaning "are you so broke it hurts?" — implying his police salary is so tight he must be tempted by bribe money from a criminal organisation. This kind of blunt, anatomical trash-talk is a fixture of friction between senior and junior officers in Korean cop dramas, used to humiliate rather than threaten.
The interview subject discloses that after losing her children she made multiple 자살 기도 (suicide attempts) before a person she calls her reason for living helped her recover. Korean dramas depicting trauma survivors referencing past attempts is common; if this content is distressing, KOSIS crisis line 1393 (Korea) or your local helpline is available 24 hours.
Using a human being as 미끼 (bait) in a 쥐덫 (mousetrap) is the metaphor the character spells out here. The 쥐새끼 (rat bastard) insult woven through it is extremely common Korean invective — 쥐새끼 literally means "rat pup" and is one of the strongest go-to curses in informal speech.
Korean elementary schools routinely assign students a daily 일기 (diary) as a writing exercise, and teachers sometimes collect and read them. The diary pages shown here are exactly that format — dated entries with weather noted at the top (맑음 means "clear"). Because teachers read them, a disturbing entry would in theory flag a child's behaviour, which is part of why this diary matters to the plot.
The detective says 자살당한 거야 — a constructed passive form meaning "was made to commit suicide" or "was suicided." Standard Korean has no natural passive of 자살하다 (to commit suicide), so forcing the grammar signals that the death was staged by someone else. Korean crime journalists and detectives use this construction specifically to accuse a third party of manufacturing an apparent suicide.
Korean schools maintain a 학교생활기록부 (school life record) for every student — a comprehensive official file covering grades, behaviour notes, club activities, and teacher observations. Unlike a simple report card, it follows a student through every school level and is used in university admissions. The note 강박 (obsessive/compulsive behaviour) written there by a teacher would be an unusual and serious annotation.
실험 쥐 literally means "lab rat" or "experimental mouse," the animals visible in the science room. The character repeats the phrase in a way that turns it into a revelation — the implication being that the people involved have been used as unwitting subjects in someone else's experiment all along. The image of lab animals sorted by diet echoes the eugenics-tinged genetic research that runs through the whole series.