At about six minutes into the program, Nathan Fillion is pulling on a pair of blue latex gloves. He does a quick set of hand motions. In a Twitter message, he states that the hand motions are a reference to the phrase "two by two, hands of blue", which comes from his program Firefly (2002).
Beckett is shown reading an advance copy of "Heat Wave". In reality the book was released on September 29, 2009, with an unknown author using the name "Richard Castle". The author's notes are written in-character and authors James Patterson and Stephen J. Cannell, who appear in the series, wrote promotional blurbs as though Castle were a real fellow author. "Heat Wave" debuted at #26 on the New York Times bestseller list.
David Ramsey and Tyler Hoechlin both play heroes in the CW superheroes series (Arrowverse). Ramsey plays John Diggle/Spartan and Hoechlin plays Clark Kent/Superman.
Castle describes pemmican as "beef and grease kind of melted together into a jerky". Almost, not quite. The beef is completely dried then crushed into a powder. Mixing that pound for pound with rendered beef kidney suet makes a paste that feels sort of like gritty modeling clay. This is high calorie, high protein, and has a room temp shelf life of several years.