With Stana Katic's absence, Nathan Fillion, Jon Huertas, and Seamus Dever are the only actors who have appeared in every episode.
Nathan Fillion and Adam Baldwin played in the Sci Fi series Firefly (2002) and movie Serenity (2005) together.
"Cool" from "West Side Story" is performed at a pivotal moment in the action, and a different version is used over the end credits.