We actually needed the memory - if you see the film - as a very different kind of a plot device of revealing some information to our main character. So we chose to represent it as these sort of beautiful little snow globes, which kind of, weirdly, that's the way we think of memories - at least, most of the folks that we talked to. You think of these memories as being very pure and absolute and unchanging. That's not actually real life.

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.

I'm not actually sure if guilt is an emotion. In fact, that was - at the very beginning of this process, we realized, man, we really don't know very much about this subject so we better do some research. And we started looking around online.

You know there's always that kid in your class — and every class has one — the kid who draws all the time and is really good? That was not me. I was a lousy draftsman. But as soon as I figured out that I could make things come alive, like using the corners of my math book to make flipbooks, I was hooked.

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.

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.

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 .