Castle Shows Referenced

Episode 2x06 (Vampire Weekend) opens with Castle putting on his Halloween costume which happens to be a costume of a "space cowboy". The costume is the exact uniform Nathan Fillion wore in Firefly. In Episode 3x09 (Close Encounters of the Murderous Kind), Castle says something in Chinese and when Beckett asks him: "A semester aboard?" he simply responds by saying "Naw, a TV show I use to love." This appears to be a reference to Firefly, where Nathan Fillion's character repeatedly spoke Chinese.

In Episode 3x09 (Close Encounters of the Murderous Kind), a mysterious case seems to indicate an alien abduction. When the body of a young women is found killed by "explosive decompression" and a book about aliens is found in the back seat of her car, Castle whistles the theme song to The X-Files. Later in the same episode, Castle makes a reference about Beckett dying her hair red and calling him Mulder.