Trivia: Castle's Halloween costume is of Malcolm Reynolds, played by Nathan Fillion in the short-lived TV show "Firefly." Alexis asks him: "Didn't you wear that like five years ago?" Serenity, the film based on Firefly, was released 5 years before this episode aired.
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: After learning a murdered television host was planning on changing his show-ending signature line, Castle suggests to Beckett that they should have a signature line of their own, and suggests "A whole new chapter in crime solving." This is actually the tag line on the season 1 DVD set. The other line Castle suggests, "She's armed, he's dangerous", became the tag line on the season 2 DVD set.
Trivia: Near the end of the episode, while dancing at the school dance, Beckett and Castle decide on Andrew Belle's "In My Veins" as 'their song' for the wedding. The same song plays under the end of "Always", the season 4 finale, when Beckett admits to Castle her feelings for him and they consummate their relationship.
Trivia: Throughout the episode, it's heavily implied, short of mentioned outright, that Castle is being considered to write a new James Bond novel. Stana Katic is actually a Bond girl, having had a small role as a Canadian intelligence officer in 'Quantum of Solace'.
Trivia: As a tie-in to the series, shortly after it premiered, ABC began publishing Castle's Nikki Heat books, ghostwritten by a real author and credited to Castle. In 'Heat Rises', a murder victim is mentioned as having owned a copy of the movie 'Air Force One', which was written by "Castle" creator Andrew Marlowe.
Trivia: Firefly reference. In that show, two agents were sent to capture the character River Tam. The agents wore blue surgical gloves and were foreshadowed by River prophetically muttering "two by two, hands of blue." In this Castle episode, after putting on blue gloves ("hands of blue") , Castle holds up two fingers on each hand one after the other ("two by two") then opens his hands.