Nathan Fillion's "Firefly" references on "Castle"

From SyFy blastr:

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.

You can see the rest on blastr