Cate Blanchett had to re-learn the piano, learned how to speak German, and learned how to conduct an orchestra for the film.
Professional cellist Sophie Kauer had no prior acting experience and auditioned at the encouragement of a friend. She learned to act by watching YouTube tutorials hosted by Michael Caine.
The screams Lydia hears when jogging in the woods are the audio of Heather Donahue from the climax of The Blair Witch Project (1999).
Todd Field wrote the film specifically for Cate Blanchett and would not have made the film without her. They had previously planned to work on a different film, but Field could not acquire adequate financing for it.
The film begins in a mono sound mix and gradually adds more tracks as it goes on.