Sia did an interview with Spin Magazine and she talked a little about working with Christina.
You helped Christina Aguilera with her new album, Bionic. Tell us about it.
She's f*cking crazy dope amazing. She's a perfectionist and she totally scrambled my mind. When we were doing the vocal production, every take was sick. Then she'd ask, "What do you think of these five takes?" I'd be like, "Well, every single one of them is perfect and I have no idea what you're talking about if you think one of them is not perfect." She's a mad scientist of singing.
You guys have the same birthday, right?
We do. Isn't that weird? Oh, and Brad Pitt, too. Dude, don't forget Brad Pitt.
http://www.spin.com/articles/qa-sia