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 .

Any great movie you watch has some element of darkness or loss or some suffering in it. That's what makes the fun parts fun.

And usually I'm not watching the screen. I'm kind of sitting and looking off to the side, spying on people to see what they react to' cause it's - as Joe Ranft used to say, you know, animation is like telling a joke and waiting for three years to see if anyone laughs

And in part that's good but then, like any emotion - and this is something we learned from the research as well - there are positive and negative aspects to all of these.

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.

They're expecting us to make mistakes, and they've set up a process that allows us to correct for that and do it again and iterate. So I think that's a real key to the films that we've made.

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.