The number of Mulder's apartment is 42, which can be interpreted as a reference to Douglas Adams' Hitchhiker's Guide. Mulder's pet goldfish were added to the set for his apartment during the run of the series, due to a script reference to the fish. "So, we got him a fish tank," explained Set Decorator Shirley Inget, "and it's kinda nice, 'cause he's got a little pet at home, you know?" ("Behind the Truth: Mulder's Office", TXF Season 1 DVD special features)