One of the paintings in Miles Bron's living room is of Edward Norton's head on Brad Pitt's body from Fight Club (1999).
Rian Johnson has stated that he briefly considered a running joke of having Daniel Craig play Benoit Blanc with a different accent each film without any explanation at all, but decided against it.
One of the books on Blanc's bathroom floor is "CAIN'S JAWBONE". A murder mystery first published in 1934, all the pages are printed out of order. It's only been solved three times.
When Netflix bought the rights for the film, a third movie also began development, again with Rian Johnson and Daniel Craig returning.
In an interview with The Atlantic, director Rian Johnson expressed his frustration over having to add "A Knives Out Mystery" to the film's title for marketing purposes, as he wanted every film to be self-contained, except for Daniel Craig's appearance. "Honestly, I'm pissed off that we have 'A Knives Out Mystery' in the title. You know? I want it to just be called 'Glass Onion.'" He adds, "I get it, and I want everyone who liked the first movie to know this is next in the series, but also, the whole appeal to me is it's a new novel off the shelf every time." However, the subtitle is only used in the film's marketing. In the film itself, the title cards say simply "Glass Onion".
Joseph Gordon-Levitt: As the voice of Miles' clock, the "Hourly Dong". He has had a role in all of Rian Johnson's films.
Serena Williams: As herself. She's holding a copy of the novel Gravity's Rainbow, which was also referenced in Knives Out (2019).
Natasha Lyonne: As herself, playing Among Us (2018) with Benoit Blanc. She suggests crosswords to Blanc to keep his mind occupied. Lyonne is a known crossword fanatic and even co-authored a crossword puzzle in the New York Times. Her cameo had to be reshot because Rian Johnson changed Blanc's dialogue, and they reshot it in Lyonne's trailer while working on Poker Face (2023).