So my first experience was that I had to do a reboot of my expectations. Like fantastic, great, he's young and charismatic and I was like wow, this is so disorienting, I have to reboot. In retrospect, I can see that it's really powerful that somebody [Snowden] so smart, so young, and with so much to lose risked so much.

One of the most frightening things, I think, is the capacity for retroactive searching, so you can go back in time and trace who someone is in contact with and where they've been.

I think one of the most shocking things is how little our elected officials knew about what the NSA was doing. Congress is learning from the reporting and that's staggering. Snowden and [former NSA employee] William Binney, who's also in the film as a whistleblower from a different generation, are technical people who understand the dangers.

People are starting to understand that the devices we carry with us reveal our location, who we're talking to, and all kinds of other information.

Snowden is almost preternaturally prepossessing and self-possessed. I think of a novelist whose dream character just walks into his or her head. It must have been like that with you and Snowden. But what if he'd been a graying guy with the same documents and far less intelligent things to say about them? In other words, how exactly did who he was make your movie and remake our world?

The most striking thing Snowden has revealed is the depth of what the NSA and the Five Eyes countries [Australia, Canada, New Zealand, Great Britain, and the US] are doing, their hunger for all data, for total bulk dragnet surveillance where they try to collect all communications and do it all sorts of different ways. Their ethos is "collect it all."

It's not everyday that a whistleblower is actually willing to be identified.