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 episode opens on a scalpel — 메스 (meseu) — the same instrument used in the earlier surgery at the centre of the plot. In Korean medical dramas and crime thrillers alike, the scalpel carries dual weight: it is both the tool of healing and, in this story, a murder weapon and a code word viewers have been tracking across the season.
The characters decode 'S.ex' as an abbreviation for 실험체 (silheomche), meaning 'experimental subject.' They connect it to 이어 펀치 (ear punch) — a real laboratory practice where mice are hole-punched in the ear to identify individuals in an experiment. The killer apparently adapted this by piercing the victims' fingers instead, since, as one character grimly notes, humans don't have the right ear shape for the standard tool.
헤드헌터 (headhunteo) is the tabloid nickname the public gave Han Seo-jun. In Korean, the word is borrowed directly from business English — a recruiter who 'hunts heads' for jobs — but the drama twists it into its literal meaning. Korean media routinely attaches catchy English-derived nicknames to notorious criminals, echoing real cases like '지존파' or '막가파' that gripped the country in the 1990s.
One detective mentions that tonight is the suspect's mother's 제사 (jesa), a ritual held on the anniversary of a family member's death. The family prepares food, bows, and pours drinks for the deceased's spirit. It is one of the most important obligations in Korean family life, so the assumption that a son might appear near his home on this night is entirely reasonable to a Korean audience — skipping one's own parent's jesa would be almost unthinkable.
The rare illness Ba-reum identifies is 세가와 증후군 (Segawa jeunghugun), or Dopa-Responsive Dystonia — a real genetic disorder caused by a mutation in the GCH-1 gene on chromosome 14. Because it causes movement problems that worsen through the day and often look like cerebral palsy (뇌성마비, noesongmabi), it is frequently misdiagnosed. The key tell Ba-reum noticed was that the patient had no intellectual disability, which is typical in true congenital CP.
Han Seo-jun describes his secret laboratory as a 판도라의 상자 (Pandora-ui sangja), Pandora's Box. The Greek myth is well-known in Korea through school curricula, and the phrase is used idiomatically in everyday Korean to mean something whose opening unleashes irreversible consequences. His use of it here is both a boast and a warning.
The investigator suggests going out for 숯불갈비 (sutbul galbi), beef or pork ribs grilled over real charcoal. It is a classic Korean comfort meal and a go-to choice for serious conversations over food — the kind of meal colleagues share when they need to talk something difficult through. Charcoal grilling gives the meat a smoky depth that gas grilling does not, and many Koreans consider it the definitive galbi experience.
The man who arranged Ba-reum's secret surgery identifies himself as 비서실장 (biseosilchaang), the Presidential Chief of Staff — the highest-ranking aide to the President of South Korea. Unlike a cabinet minister, this person is not subject to National Assembly confirmation, giving the role quiet but enormous practical power. The drama uses this to explain how such an illegal operation could be arranged and hushed up.
The reporter points out that a detective who had access to a firearm used a scalpel — 메스 — instead. In Korean forensic reasoning on screen and in real investigative culture, the choice of weapon is treated as a window into the killer's psychology and purpose. A gun suggests distance and decisiveness; a scalpel up close suggests something far more personal or deliberate, and it plants doubt about whether the arrested detective is actually the killer.
The team pulls up records of children reported missing in a specific county (구령시) in 1994. South Korea has maintained national missing-persons registers since the 1980s, and cold-case child disappearances from the 1990s remain a deeply sensitive topic — the 이형호 사건 (1991) and others left lasting public trauma. Matching a decades-old missing-child file to a current case is a plot device that resonates strongly with Korean viewers who grew up aware of those unsolved cases.
The prison officer casually refers to his girlfriend's parents as 장인 (jang-in) and 장모 (jang-mo) — the formal terms for father-in-law and mother-in-law — even though the couple hasn't had a wedding yet (식도 안 올렸는데). In Korean, using these terms before the ceremony is a small social slip that signals how thoroughly he already thinks of her family as his own, which is why his colleague teases him warmly about it.
People greet Ba-reum as 국민의 아들 (gungmin-ui adeul), literally 'the nation's son.' Korean media and internet culture frequently crowns ordinary people with affectionate superlatives — '국민 첫사랑' (nation's first love), '국민 남동생' (nation's little brother) — when they do something that captures the public's heart. For Ba-reum, whose story of recovering from a horrific injury played out on TV, the title signals he has become a feel-good public figure, which is deeply ironic given what the audience now knows about his brain.
Ba-reum notices that items linked to the priest and to Bong-i's grandmother — a crucifix necklace and a brooch — appeared at the scene and then vanished once another officer arrived. In Korean crime investigation procedure, 현장 보존 (scene preservation) is a formal requirement; objects appearing and disappearing point to deliberate planting by someone with access. The episode closes on Ba-reum concluding that a 진범 (jinbeom), a true culprit separate from the arrested suspect, is still at large.