In the second scene at Beckett's apartment Castle tells Beckett, "I don't hang around here just to annoy you." and a few lines later she asks, "So why do you keep coming back, Rick?" This scene plays off a scene in the pilot where they are looking through his fan mail. In that scene she asks him, "Why are you here, Rick? Are you here to annoy me?". These were the only times she called him Rick to that point.
When Castle and Beckett are talking in her apartment, after she tells him to go home, he says "fear does not exist in this dojo". This is a famous line from the movie The Karate Kid (1984).
During their meet at the coffee shop, Raglan mentions that Beckett's stand-off with Dick Coonan in the precinct happened "about a year ago". The episode aired almost exactly a year after "Sucker Punch (2010)", missing the anniversary of its airdate by just six days.