Beckett's now-famous "Shut up!" and Lanie's line to the corpse "you may not see it but I do" were both improvised.
About twenty minutes into the episode, Castle and Beckett have a conversation in an elevator about Castle and Kyra that mirrors their conversation, with the roles reversed, about Beckett and Will Sorenson in "Little Girl Lost (2009)".
A. Millano and N. Fillion, have utilized a shared PR photo to add authenticity to their characters backstory, the origin of the irl photograph could be the result of either a 'Charmed', cast party invitation or a The Outer Limits (1995) season invitation the only TV show prior to this episode that they both worked upon.