Trivia: In this episode, Castle says the words "My partner is crazy and may start firing at any moment" in Chinese. Beckett then asks him "Semester abroad?", to which he replies "Nah, a TV show I used to love". This is a reference to Firefly, a TV show starring Nathan Fillion in which characters occasionally spoke in Chinese.
Trivia: When Ryan and Esposito go to where the victim worked, the guy that talks to them was on an episode of the short TV series Moonlight where he played a guy that was stalking a girl after his death. He even tells Ryan that if he changes his mind, he'll give him some hair gel and fangs; the guy was turned into a vampire before his execution.