... on Spike Jonze's HER:
Samantha Morton was originally the voice of Samantha. She was present on the set with Joaquin Phoenix every day. After the filming wrapped and Spike Jonze started editing the movie, he felt like something was not right. With Morton's blessing, he decided to recast the role and Scarlett Johansson was brought and replaced Morton, re-recording all the dialogue..
Jonze's friend Steven Soderbergh helped him trim the film by cutting down an early version of it from two-and-a-half hours to 90 minutes...all in twenty-four hours' time.
Amy Adams said writer/director Spike Jonze would essentially lock her and Joaquin Phoenix in a room together for an hour or two every other day, and make them talk to each other. Jonze did this so that the actors could get to know each other better. Adams credits this for her and Phoenix's close friendship.
This is the only movie Spike Jonze has written as well as directed, completely from his own original script.
Carey Mulligan was originally cast but dropped out due to scheduling conflicts. She was replaced by Rooney Mara.
Chris Cooper filmed a few scenes but his role ended up completely cut from the final movie.
During some of the more emotional scenes, Amy Adams would sing songs from famous musicals like "Annie" and "The Rocky Horror Picture Show" in order to cheer herself up. Eventually, Joaquin Phoenix would join in and they would sing together. However, they stopped after they saw Spike Jonze filming them.
[From Indiewire/The Playlis interview]
It’s funny, you take this beautiful woman, but you don’t even show her onscreen. Why Scarlett? Other than her voice which obviously has that sultry lower register.
Definitely. The timbre of her voice is beautiful. It's the person inside the voice, it's her intelligence, and it’s her wit. She's the kind of person that can tease you and get right to your core but also it’s affectionate. You want to get teased by her. How do you define charisma, true charisma? She's obviously beautiful, but you take that away and she's just as captivating. She's got that thing and combined with the emotional depth of where she's willing to go—she really went there in this incredible way.