Well, what we do is we have a script, of course. But for us, writing is also like storyboarding. It's drawing. And so we will cut all of those drawings together with music, sound effects and dialogue. And we screen this kind of stick-figure version of the film.

When I was in middle school, I liked to make cartoons.

And as I was sort of doodling, I was thinking, surprise and fear - probably fairly similar so let's just lose surprise. And that left us with five.

If you were feeling sad right now and you recall a sad - or, a very happy memory from the past, it will be tinged with more sadness based on your current feeling. So we felt like that was actually on solid scientific ground .

It is one of those weird social things. Even as parents we say, oh, don't be sad. You know, come here, we'll distract you with some ice cream or something. And I don't know if that's always the best thing. But it's certainly - you understand why people do it.

Dr. Paul Ekman, who worked in San Francisco - still does - which is where Pixar Animation Studios is, he had early in his career identified six. That felt like a nice, manageable number of guys to design and write for. It was anger, fear, sadness, disgust, joy and surprise.

But the truth is, at some point, our films - almost every single one of them - are really bad. And it's largely hats off to John Lasseter and Ed Catmull who have set up a system whereby they're expecting it.