SawWriter and star of the smash hit Saw, Leigh Whannell, describes a typical serial killer movie as being “Ashley Judd leaning over a body saying ‘I think I know him’.”

Like historical war movies and romantic comedies, there’s very seldom anything new on offer in serial murderer thrillers.

It’s always about a sensitive and talented detective who discovers the particular quirk of the killer (whether he’s copying the crimes of famous murderers, taking over his victims’ lives when he kills them or making suits out of their skin). They close in on him until it inevitably gets personal and leads to the climatic showdown, the police backup arriving in time for the victorious hero to wander dazedly out of the warehouse, tenement or power plant.

“In Saw, we were particularly inspired by the films of David Lynch,” a tired-looking Whannell describes, on the last leg of a worldwide publicity tour with director and work partner James Wan.”The atmospheres in his movies are so scary. Somehow he manages to make one scene more terrifying than most horror films manage to do in the entire running time.

“We also love Dario Argento, but those guys aren’t very mainstream. For Saw we were thinking more mainstream or conventional, but we wanted to take some of the bizarre elements from Lynch or Argento and put them into a more accessible storyline.

“Rather than the standard thriller you’ve seen a million times before, we wanted to inject something a little surreal into it. We wanted it to be cultish, but somewhere between the surreal and the real.”

The story of Saw is now legend in Hollywood and RMIT University, Melbourne, where the two studied and came up with the idea for it. When told by their manager that a trip to America to sell the script might be prudent, they went ahead and shot one of the scenes to be (as Whannell puts it) their calling card.

“It was the jaw trap scene,” Whannell says, referring to one of the grislier sequences that appears in the finished film.”We had the script — which we tried to get made in Australia but couldn’t — so we took one scene out of it and just shot it. We had the script in one hand and a DVD of the scene in the other, and that’s what led to the film being made.”

But wait a minute; surely they must have a friend on the board of Lions Gate Films or something — how on Earth do two film students from Melbourne get their script in front of the people who can (and have) sent it to number three in the US, making over $50m so far?

“There are a lot of gatekeepers in Hollywood,” Whannell concedes,”but the easiest way to get through to them is to give them something good, something they want. Then they’re suddenly very welcoming. It wasn’t hard for us because they wanted our script so it was a case of them wanting to be in business with us.”

It’s a low budget film — sets were (in the words of director Wan) being torn down around them for subsequent shots. Both star and director say it was just like doing a student film back at school (albeit with Danny Glover and Cary Elwes). How has it come to be such a staggering success along the lines of The Blair Witch Project or Open Water?

“The only question the audience has to ask themselves is ‘what’s going to happen next?” is Whannell’s take on it, and that’s what Saw does at every minute.

The plot isn’t without its weaker links, but from the opening frames where two men wake up in a filthy industrial bathroom block, chained to opposite ends of the room with a dead body in between them, you’re on the edge of your set waiting to see what it’s all about.

If you love mysteries, the story will keep you gripped. If you love imagery, director Wan grasps a Se7en-inspired visual of filthy water, clanking metal and the stink of fear and malice beautifully.

Confrontingly violent at times (though not as gory as you’ll remember because of the high shock quotient), Saw looks initially like it’s just the story of two guys who wake up chained to bathroom walls with a tape in their pockets that contain cryptic messages from their captor.

One scene at a time, the mystery is peeled back to reveal how they came to be there and what they have to do with each other. Exposition and action are wound so tightly together your attention will never slip.

Whannell and Wan are two filmmakers who deserve the success Saw has gained for them around the globe because of three yardsticks with which to measure it; the idea, the story and the execution. Each one is as strong and distinctive as any established Hollywood studio hack has ever come up with.