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.
Korean media often gives serial killers a dramatic nickname based on their method, the way tabloids coined 'Jack the Ripper.' Here the broadcaster dubs Han Seo-jun '헤드헌터' (head-hunter) because he decapitated his victims. The nickname is used in official press briefings and becomes the public shorthand for the entire case.
A bystander says the woman took pills intending to die together with her unborn child — a practice Koreans call 동반자살 (dong-ban ja-sal), literally 'companion death.' It is treated as a distinct and especially tragic category of suicide in Korean news and law, carrying its own moral weight separate from a single person ending their own life.
Go Mu-chi stumbles to Ba-reum's door blackout drunk and ready to fight — a recognisable pattern in Korean dramas where a man drinks himself into a rage rather than sit with grief. Drinking alone to the point of memory loss (필름이 끊기다, 'the film cuts off') is acknowledged culturally even while being socially criticised, which is why Ba-reum scolds him directly rather than tiptoeing around it.
The professor explains that only the damaged portion of Sung Yo-han's 전두엽 (jeon-du-yeop, frontal lobe) was grafted into Ba-reum's brain. In real neuroscience this is impossible, but the drama uses it as its premise: because the frontal lobe governs impulse control and personality, the transplant raises the horror-story question of whether a killer's character can literally invade another person's mind.
The detective quotes the phrase 눈에는 눈, 이에는 이 (nun-e-neun nun, i-e-neun i), the Korean rendering of the Old Testament lex talionis. It is widely known in Korea through the Bible and through frequent use in dramas, courtroom rhetoric, and everyday speech when someone wants to justify matching punishment to crime — here used as a half-joking threat to an aggressive neighbour.
The detective notes that Woo Hyeong-cheol was a fifth-grade elementary student, 12 years old, at the time of the crime. Korean schools run grades 1–6 for elementary (초등학교), and children enter at age 8 in Korean age — roughly 7 in international age. Korean age traditionally adds one year at birth and another each New Year, so a Korean '12-year-old' is usually 11 by Western count, meaning Hyeong-cheol was very young when he first tied a victim's hands.
Go Mu-chi's flash of inspiration links a supermarket's cold-chain problem to Hong Na-ri's refrigerator. Koreans typically keep a separate kimchi refrigerator (김치냉장고) calibrated to very low, stable temperatures, and household fridges are expected to stay consistently cold. The idea that a large pot of simmering 사골 (sagol, beef bone broth) could knock a refrigerator's contents out of safe temperature — spoiling milk inside — is the everyday domestic logic that cracks the alibi.
Oh Bong-i teases the detective by asking whether he is a 제비 (je-bi, literally 'swallow'), Korean slang for a young man who lives off an older or wealthier woman's money. The word entered popular culture in the 1990s and recurs in dramas to describe men perceived as charming but financially dependent — the joke lands because the idea of the gruff, middle-aged detective playing that role is absurd.
The uncle explains that hydrangeas (수국, su-guk) turn blue in acidic soil rich in iron and purple/pink in alkaline soil treated with 석회 (seok-hoe, garden lime). This is real horticultural chemistry. Ba-reum immediately connects 'iron-rich acidic soil' to buried metal — a murder weapon — making the flower-bed an unlikely but scientifically grounded clue. Koreans often grow hydrangeas in home gardens, so the uncle's casual explanation feels ordinary until its significance clicks.
The killer has been winning the trust of runaway teenagers (가출 청소년, ga-chul cheong-so-nyeon) by offering free counselling and helping them return home — presenting himself as a civic-minded 변호사 (byeon-ho-sa, attorney). In Korea, lawyers carry significant social authority; a volunteer who reunites families with their lost children would attract almost no suspicion. The drama uses this cultural blind spot to show how the killer selected vulnerable victims.
Woo Hyeong-cheol claims the first death was a knot-practice accident he learned in 보이스카우트 (Boy Scouts, which has operated in Korea since 1922 and is a mainstream after-school activity). The specific knot mentioned is a 산악 구조용 매듭 (mountain-rescue knot), taught in outdoor skills training. The alibi sounds plausible to a grieving father precisely because Scout knot practice is so ordinary in Korean childhood.
Woo Hyeong-cheol says the late Dr Daniel told him he was born a 사이코패스 (sa-i-ko-pae-seu, psychopath) — echoing the drama's recurring question about whether violent behaviour is genetic destiny or a choice. This mirrors real Korean public debate sparked by high-profile crimes, where broadcasters and academics argue on air about whether serial killers are 'made' or 'born.' The drama deliberately leaves the answer unsettled.
After Ba-reum beats Woo Hyeong-cheol nearly to death, the killer whispers 짜릿하지 (jja-rit-ha-ji, 'feels electric/thrilling, doesn't it?') — goading him into accepting that he enjoyed it. The word 짜릿하다 is used for innocent thrills (a cold drink, a sports win) and for something darker; using it here forces Ba-reum — and the audience — to confront whether the violence felt good, tying directly back to his fear that Sung Yo-han's brain is reshaping who he is.