As a detective who solves murder cases, it makes sense that Poirot would consider murder an unforgivable offense—though later events in the story reveal that Poirot’s morality is not as black-and-white as it might first seem. Jacqueline’s admission that she wants to press her pistol against Linnet’s head and pull the trigger is startling, especially since she’s confiding in a murder detective. Perhaps Jacqueline is playing a strategic game of some sort, but it seems more likely that regardless of what she is or isn’t plotting, she’s starting to become a little unhinged.