In "I Am the Pretty Thing That Lives in the House," Polly is killed due to the vengeful spirit of a former resident, Iris Blum, who becomes malevolent after her death. Polly, a caregiver for Iris, is ultimately targeted as the spirit seeks retribution for her past. The film explores themes of isolation and the haunting nature of the past, with Polly's demise serving as a culmination of the supernatural events tied to the house's dark history and Iris's unresolved issues.

"I Am the Pretty Thing That Lives in the House" is a psychological horror film that explores themes of fear, mortality, and the supernatural. While it may not have a single line that is universally recognized as the "most famous" in horror, many iconic horror films feature memorable lines such as "Here's Johnny!" from "The Shining" or "I see dead people" from "The Sixth Sense." The impact of a line often depends on its context within the film and its resonance with audiences, creating lasting impressions in the horror genre.