I think the closest thing I can come to defining what that vital thing is for me - is that there's a sort of soul-quality in writing, if it's any good. It has a spirit or an energy to it that is very integral to who the writer is on a deep level. It's almost a cellular thing. It takes place in the cells of the writing, and it is what makes it alive or not.
Once we were on the set, we each did different kinds of work. I was doing more the technical stuff, the framing and the camera work, and she was working more with the actors. Marjane [Satrapi] and I don't stop speaking once we're on the set. We continue to talk. We define what our roles are going to be on set, because to have a snake with two heads is silly.