It was Don Johnson's idea for his character to hand his empty plate to Marta as if she was the maid during the immigration conversation.
Jacob's line "You had sex with my grandpa, you dirty anchor baby!" was improvised by Jaeden Martell, but it was originally lost in the scene since multiple characters were talking and yelling. Michael Shannon noticed this and approached Rian Johnson, telling him that Martell had a killer line, so they made sure to go back and capture it.
Rian Johnson kept strict control over how much each actor knew about the script to make sure those playing characters in the dark were as confused as the people they were portraying.
At the will reading, Ransom tells his family to "eat shit": he was originally scripted to tell them, "Fuck you." Rian Johnson decided to remove most of the "F" bombs in the script to secure an MPA PG-13 rating and to keep the movie more like the mystery films he used to watch with his family growing up. Chris Evans was the one who suggested substituting "eat shit."
Rian Johnson said that Michael Shannon was by far the funniest person on set, and came up with a lot of his character's funny lines and physical moments, such as his triumphant arm-raise during the "eat shit" scene, and his retort: "I am not eating one iota of shit!"
Joseph Gordon-Levitt: Joseph Gordon-Levitt provides the voice of the police detective heard on the television series Marta's sister is watching. The character is billed in the film's credits as Detective Hardrock. Gordon-Levitt has appeared in six of the films Rian Johnson has directed.
Gary Tanguay: When the news crews gather outside Marta's home, a clip is shown of a reporter on the TV broadcasting from outside the house. The reporter is a local New England sports talk show host.
Rian Johnson: [cousins] Rian's cousin Mark Johnson did the title credits and based the font on an Agatha Christie series of paperbacks. Zack Johnson is another cousin, and he painted the cast paintings for the end credits.
Rian Johnson: [music] Rian's cousin Nathan Johnson, composed the film's score, as he's done for all of the director's films "except Star Wars: Episode VIII - The Last Jedi (2017), which he understood." It was the composer's first time using an orchestra.