The episode's title "Windmills" is a reference to the Cervantes novel "Don Quixote", where the hero, a delusional man who thinks he's a knight, tries to tilt, ie joust, with windmills who he perceives as malevolent giants. The phrase "tilting at windmills" has come to mean fanciful or fruitless striving. Holden's mother says that Don Quixote was one of his favorite novels as a child but that he never understood the work's thematic message.
Use of the code word "ubiquitous" to indicate one's status covertly had also been done in the novel "Leviathan Wakes," upon which the first season is based. In that situation, Fred Johnson wanted Holden to slip it into the first sentence of his response to Johnson's message to show he wasn't under duress.
Shohreh Aghdashloo and Frances Fisher were born on the same day, May 11, 1952.