• The film is often interpreted as a metaphor for mental illness, particularly dissociative identity disorder (DID) or schizophrenia. Su-mi's fragmented perception of reality, her imagined interactions with her deceased sister, and the blurred line between hallucination and truth suggest a mind grappling with trauma. The stepmother, Eun-joo, may represent an externalized manifestation of Su-mi's guilt or self-loathing, embodying the 'monster' she fears she has become.
• Some analysts argue that the film critiques patriarchal family structures and the suppression of female voices. The stepmother, Eun-joo, is initially framed as the villain, but her character may symbolize the scapegoating of women in abusive or dysfunctional households. The father's passivity and eventual complicity in the family's secrets reinforce the idea of systemic silence around domestic trauma.
• The recurring motif of the 'red dress' worn by the ghostly sister, Su-yeon, has been linked to themes of martyrdom and unresolved grief. In Korean culture, red is associated with both celebration and death, and the dress may symbolize the inescapable presence of the past. The film's nonlinear storytelling could reflect the cyclical nature of trauma, where the past and present are indistinguishable.
• A less explored theory posits that the entire narrative is a supernatural ghost story, with Su-yeon's spirit genuinely haunting the household. The film's ambiguity leaves room for this interpretation, particularly in scenes where Su-mi interacts with her sister in ways that defy logical explanation. The stepmother's cruelty and the father's neglect may have created a 'haunted' environment, where the dead linger due to unresolved emotional pain.
Two sisters return home after a stay in a mental institution, only to face disturbing events and a strained relationship with their stepmother. As eerie occurrences unfold, dark family secrets begin to surface, blurring the line between reality and nightmare.