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.

I mean, I've - these other films were flukes. I don't know what I'm doing. I should just quit. What would I miss? I'd miss my house and I'd miss going to work. But I think the thing that I realized I would miss most is probably similar to everybody, which is your friends.

And it sort of hit me that the very subject matter of the film that I'm dealing with is the key to the most important thing in our lives, and that's our relationships. And so we had done all this research showing the job of each individual emotion, you know, fear keeps you safe. It deals with uncertainty.

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.

Anger is about fairness. If it feels that you're getting ripped off or taken advantage of, that's when anger comes up. Sadness deals with loss. And I suddenly had this new revelation - it felt like to me - that those are all true, but the real, deeper reason we have emotions is to connect us together. And that felt big to me.

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.

It might have been introduced slowly over the course of the years as you recall this memory over and over. So that was a very cool but complex idea that we thought about representing in the film but could not find a way to make it work.