Q: Even without that, it raises a lot of questions since: What is the soul? What if you could "borrow" someone else's? Whose soul would you order from the catalogue of anonymous donors?

A: You know, on the set that they had, they actually had catalogues, and the detail was amazing. It was hilarious. They had like, Yugoslav gymnast, for instance. It was so amazing that they went to all that trouble, and you never even see it [as a viewer]. But when you take on someone's soul, you get hyper-empathetic. At one point, the soul mule tells me, "I really like your soul," because she carried mine. And I get that way, too, about the Russian poet's soul.

Q: Funny how someone else's soul always seems better than your own...

A: That's probably true -- somebody else's soul feels more beautiful. But I suppose if you had Stalin's soul put in you, you probably wouldn't like it. But you never know -- maybe there was something beautiful in there once. And I like that the appearance of the physical soul is more important than anything else in the movie, when really, the appearances shouldn't matter at all. If it looks like a chickpea, a jelly bean, an orchid, or whatever, it doesn't actually matter.

Q: So much emphasis is placed on the career of the soul donor. Do you think that matters? Maybe for the Russian poet, sure, but the gymnast?

A: Well, certainly as a marketing tool, that's a way to sell someone on a soul. How much it actually has to do with it? I suppose the pressure of your job creates an environment for your soul and probably shapes it. That's an interesting thought, whether it's immutable. Did Stalin have a nice, minty soul and it never changed, he did? It was just the job! That's all! [Laughs]. If he had just been a farmer, it would have been OK.

Q: Or if Hitler been successful at painting...

A: If he'd just been allowed to paint postcards! [Laughs]. You wonder if he just started out that way, or not. I get the feeling those guys started out that way. If there's a soul, I suppose the soul would start out that way.

Q: Is acting a bit like borrowing a character's soul?

A: It becomes trickier for real life people. Harvey Pekar in American Splendor is real, and it's a question of whether I think about the performance and the character, or Harvey. He's got a lot of soul. I don't know what it would look like. Like a chocolate milkshake or something. Miles in Sideways, he has a soul, but it's not in good shape. It's just a little twisted.

Q: What about Philip K. Dick, who you're supposed to play sometime soon...?

A: That's a project that's been around, and I've looked at a lot of different versions [of scripts], and none of them have been quite right. It's a waste of time to do a straight biopic for him. Hopefully they'll come up with something, because there's a lot there. Would you want to have Philip K. Dick's soul, though? I'd want his imagination, his brain, but that's probably intimately connected to his soul. He had a tough time, that guy, so I don't know about his soul. To just play him is nice. I don't have to be him.

Q: Is that why the Paul Giamatti of this movie isn't really biographical? In the movie, your wife is named Claire, and she's played by Emily Watson, while your real-life wife Elizabeth was on hand as producer...

A: I didn't want any verisimilitude. At one point, Sophie added some sort of actual biographical detail, but I just wanted it to be a character. As much of a character as I could keep it to, I wanted to. My wife would have never played herself anyway. So there's me, and then there's my performance of me. I think that's part of the idea. It's meant to keep you a little bit off balance.