After going out to dinner with Meredith, Beckett makes Castle promise that, as long as they're together, Meredith never stays at the loft again. This actually ended up being Meredith's final appearance in the series.
When he's stressed, Castle has a subconscious habit of leaning to the left.
Nathan Fillion (Richard Castle) and Darby Stanchfield (Meredith) play characters who were previously married to one another. In the movie Waitress (2007), they played husband and wife.
The story of Billy Pipen, one of the clients of the suspect's attorney, can roughly be compared with the death of Natalie Wood, who also fell out of a boat and drowned. Her husband at the time, actor Robert Wagner, was suspected of being involved in the death of his wife to the point of the case being re-opened in 2011, but he never was formally accused. Wagner was officially ruled out as a suspect in 2022.
Guest actors Nancy Lee Grahn and Jack Wagner worked together on the soap operas Santa Barbara (1984) and General Hospital (1963). On Santa Barbara, she played his aunt.