As anyone who's been on the Internet for the last week knows, Nathan Fillion and Firefly are still attached at the hip. And even though he's got a hit crime procedural on ABC, the once and future (if he has his way) Mal Reynolds can't help but sneak his love for Joss Whedon's cult hit into his new gig.

The references started in Castle's second season, after the fear of another Fillion show not making it past a first season faded.