The climax involves a scene of body horror—the cutting out of a tongue—that serves as a symbolic payment for the sins of the tongue (gossip and loose speech) that began the cycle of tragedy. It is a moment of operatic self-mutilation that underscores the film’s themes of atonement and cyclical violence.
For academic or deep-dive analysis into Park Chan-wook’s 2003 masterpiece Oldboy -2003-