Nolan says this was his first knife fight, but he was previously in a knife fight in episode 2x7, "Safety," at the hospital when giving a safety demonstration to expectant mothers and the ex of one of the women showed up with a knife. He sustained a cut along his forearm.
Michael Graziadei (Sergeant Mark Murray aka "The Cook") played the boyfriend of the murder victim in Castle S.1 E.2, sharing screen time with Nathan Fillion; however not sharing any screen time with him in this episode The Rookie.