O'Brien wrote some of the series' most acclaimed episodes: "Marge vs. the Monorail" and "Homer Goes to College". The show was initially a highly realistic family sitcom; after O'Brien's debut, the show took a rapid shift in the direction of the surreal. O'Brien also has sole writing credits on "New Kid on the Block" and "Treehouse of Horror IV", on which he wrote the episode wraparounds. Wallace Wolodarsky described a "room character" Conan put on for the writers: "Conan used to do this thing called the Nervous Writer that involved him opening a can of Diet Coke and then nervously pitching a joke. He would spray Diet Coke all over himself, and that was always a source of endless amusement among us." During his time at "The Simpsons", O'Brien also had a side project working with Smigel on the script for a musical film based on the "Hans and Franz" sketch from "Saturday Night Live", but the film was never produced.