Paranormal Activity is the micro-movie that’s been soiling America’s pants. How? Why? Director Oren Peli tells Total Film his darkest secrets...

At Paramount studios in LA, indie horror hit Paranormal Activity is screened to a group of seen-it-all film critics, who, as the credits roll, are stunned into a near-catatonic state.

The tension is broken by one man with a simple, loud and yet wholly appropriate exclamation: “Holy shit!”

Across the US on limited release, and at the Screamfest and Slamdance festivals, the movie made for $15,000 in 2006 by first-time writer/director/producer/editor Oren Peli got similar responses.

Cut to ’09, and it’s getting a full release, with Steven Spielberg’s endorsement.

The film itself couldn’t be simpler: a couple sense a presence in their home, so buy a camera and set it up at the end of their bed to see what it captures during the night.

The audience views what the camera views, and it’s become the freshest horror hit since The Blair Witch Project scared a generation a decade ago.

So what does it take to make a truly horrifying horror movie?

In a conference room at Paramount, the softly spoken high-school dropout – who came to the US from Israel as a 19-year-old to be a computer programmer – takes us through his (spooky) 13 steps...

Tools required: a camera, some actors, some kind of set (one room will do) and a vivid, sadistic imagination.

1)  Have no training

"Maybe the secret to the success of this film was that I had no real training in film making, so I didn’t know what I was supposed to do and what I was not supposed to do.

"I just set it up in a way that I knew was not traditional."

2)  Know your influences

"I always liked anything that feels natural, not scripted, so The Blair Witch Project really did the best job in the horror movie genre.

"But even movies like Spinal Tap or scripted movies like Traffic, which are done documentary style, I just love. I knew that was the style I wanted to do."

3) Think vulnerability, familiarity and invisibility

"The scariest thing is the idea of something happening while you’re asleep – you have no idea what’s going on, you’re totally vulnerable.

"Then anything that’s invisible is scarier than something right in front of you, because you don’t know what it looks like, what it wants or where it is.

"The last thing is when something happens in your home. You’re supposed to feel safe at home and you can’t escape it."

Next: Go deeper, careful casting, small budget