The film is available on several streaming platforms, including: Rakuten Viki (with subtitles).

The story follows , an aspiring but struggling writer living in unit #401. Desperate for a winning idea for a screenplay competition to help her family's finances, she becomes obsessed with a persistent "thudding" noise coming from the apartment above her, unit #501.

: Encouraged by a friend to write about her surroundings, Eun-soo begins tailing and wiretapping her neighbor, Ho-kyung , hoping his secrets will inspire her work.

: As her obsession grows, Ho-kyung notices her presence. What starts as a hunt for a story descends into a tense game of cat-and-mouse that uncovers a dark reality about her neighbor. Key Cast & Production

(Korean: Sais-sori / 사잇소리) is a 2022 psychological thriller directed by Kim Jeong-uk. It explores themes of urban claustrophobia, obsession, and the thin line between creative inspiration and dangerous voyeurism. Core Premise & Plot

as Ho-kyung: The enigmatic and increasingly threatening upstairs neighbor. Director : Kim Jeong-uk. Runtime : Approximately 106–107 minutes. Critical Reception