Neil Marshall, British director of The Descent, isn’t very good at keeping trade secrets.

For instance, the movie that American audiences see is different from the version that scared Europe silly last year. And the Appalachian caves that the movie is set in? Not in Appalachia. Not real caves even.

The film, about a group of twentysomethings — all women — who are into extreme sports, and find themselves trapped in a cave in Appalachia, is all the buzz among Internet-horror fanboys, Clint Morris of Australian site moviehole.net, among them. He calls Descent “the most effective cinematic chiller since Alien.”

We caught up with Marshall more than a year after his movie played overseas.

Q. What have you learned about the differences between American audiences and European ones, at least in terms of what Hollywood wanted you to do to your movie?

A. Every audience is different, and American audiences prefer at least a glimmer of hope at the end of their movies, one this film doesn’t really offer. We tried a new ending, because the original ending had split audiences everywhere — those who loved it, and those who hated it. Essentially, the movie’s just a minute shorter. And it’s not like U.S. audiences won’t see the original version. That’s what DVDs are for.

Q. Having grown up near Appalachia, I have to compliment you on faking it so well.

A. You know, my only experience of Appalachia comes from The Waltons, and Deliverance. Never actually been there. We shot this in Scotland. Not a real cave in it. All done on a cold, cold soundstage in Pinewood Studios.

Q. The caving and spelunking details you have in it are pretty convincing.

A. We wanted to make it as authentic as possible, so we had a caving expert on set. We took a few liberties, though. Why would they have ice axes? Not a necessity for this kind of trip. But you never know what you might run into in a cave. In Appalachia.

Q. The group dynamic really drives this. Which came first, the boogeyman, the cave or the women who face the boogeyman in the cave?

A. The location came first. The idea of doing a horror film in a cave seemed pretty unique [at the time, The Cave hadn’t come out]. What a perfect environment for a horror movie! Repellent, with mud, closed spaces, wet, cold, dark.

Then, we thought, “What if it was an all-female group?” Women in a brutal horror-action movie. “What might their group dynamic be?”

Finally, we came up with “the crawlers,” the idea that this cave might be home to something that could get the women, something human, but not quite.

And that created the movie’s structure. I wanted them to go through the … caving, first. And then, just when you think it can’t get any worse, I make it worse.