Highlights from the Project Hail Mary director's commentary:
Grace waking up from the coma was the first shot they filmed for the movie! They wanted Ryan to feel eased into the character, and what better way to do that than have him play a character who can't remember who he is?
The little "GOOD LUCK!" note in sharpie that's written on Grace's sleeping bag was canonically written by the other astronauts on the I.S.S. before the Hail Mary crew got put into the ship. In real life, Phil and Chris wrote one word each. They said it was like "a blessing on the movie."
Ryan's most nerve-wracking day on set was when he had to shoot with the classroom full of children. Most of the kids were made up of the children of the film's crew members.
The scene where Grace looks through Yao and Ilukhina's photos is footage of him looking at and reacting to actual pictures of the actors with their loved ones.
When Grace calls Stratt to tell her that he and Carl figured out how to breed astrophage, Ryan is genuinely calling Sandra on her day off set, and her audio is her genuine reaction to the unexpected line: "Carl and I made a baby!"
"We like showcasing Ryland Grace's social anxiety while having a lot of people staring at him. LOL!"
Their intention for the space funeral scene was to have Grace convey that he was trying to ease his own sadness by making the dead people with him feel better about being dead :(
The markings on Rocky's body convey his mission patch, his rank in the crew, his wedding band, and his family crest.
Grace and Stratt's conversation on the boat is Grace asking her if they're allowed to be close friends, and the response from Stratt is no, they can't. This gets driven home in the karaoke scene. She understands the value of connection, a part of her wants it, but "Her love for people has to be suspended for her to do her job."
Rocky has different forward-facing faces for different thought processes! They named his "satellite dish" face, his "scrunched up thinking face", and his "monobrow face".
Direct quote: "I love how on the spectrum Rocky is." ROCKY AUTISTIC CODED CONFIRMED!
After Rocky recovers from his injuries: "As Rocky returns to the movie, the lights turn on. The warmth returns. It's like the day breaking."
Confirmed that when Grace and Rocky reunite, Rocky says to Grace, "You came back for me, question?"
They throw this out there for two seconds and do NOT expand on it, but according to Andy Weir, Stratt is imprisoned for life but somehow ESCAPES???
The Eridians built Grace an artificial tree in his enclosure because Rocky knew he liked trees
There's so much more they shared about film processes and the people who were behind making certain effects possible. I highly recommend checking out the commentary if you're able!