It's, like, you know, if you're sad, it's a way of connecting with other people. And we - a lot of times we sort of feel embarrassed by being sad, and we go off by ourselves to hide and cry by ourselves. But, really, it's a way of re-establishing relationship.

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.

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.

The way real memories work, from what we understand, is really complex. And it's an interconnection of different things and redundancy in the brain. So the idea of a memory existing as a little snow globe - the way we represent it in the film - is actually not scientifically accurate at all.

The drive of the story is sort of hinted at the beginning, is Joy and Sadness and those two characters. Especially Joy starting to understand that there's more to life than being happy. And so that's based on real life observations and things that we've learned as adults.

It's like you run into this dark tunnel, trusting that somewhere there's another end to it where you're going to come out. And there's a point in the middle where it's just dark. There's no light from where you came in and there's no light at the other end; all you can do is keep running. And then you start to see a little light, and a little more light, and then, bam! You're out in the sun.

We've tried to regulate things so that you at least get to go home at night and not have to pull all-nighters and see them on weekends and things. So, you know, like everything in life, it's a balance.