In "Lamb to the Slaughter," Roald Dahl chose to end the story with the detail "And in the other room, Mary Maloney began to giggle." This ending serves to create a sense of irony and a contrast between the innocence and guilt of Mary. Up until this point, Mary has been portrayed as a dutiful and loving wife, who is shocked and devastated by her husband's announcement that he is leaving her. However, the final detail of her giggling suggests that she is not as innocent as she appears, and that she has a hidden, darker side. This ending leaves the reader with a sense of unease and uncertainty about Mary's true nature, and adds an additional layer of complexity to the story.