There wasn't space to mood-up. I think Rose Byrne was just extraordinary. Talk about a character that could be really unsympathetic at times. She just jumped in these scenes that go from anger to hysteria to crying to laughing and back to anger. I just marveled.
Really, for me, it's important to know who's pitching and who's catching - just what that scene is supposed to accomplish in terms of storytelling. That being said, on the day, basically what you're trying to get yourself into an open place. And if the character is in a state of anxiety or vulnerability, you try to find some touchstone.
Sometimes when you have to go into something, unless you're gifted and can just turn it on and off like a jukebox, you find someplace where there's nothing going on to get yourself into whatever state your character is entering into.
You just can never count on a formula, on a movie that you think is going to be a big hit, and that's why you do it. You have to choose each one for what you think you'll learn and the fun you'll have. And maybe the cool people that you work with or a character that you're going to be able to explore ... You just keep your fingers crossed.