TORONTO - It takes a while to puzzle through what it is we're looking at, here on the Toronto set of the low-budget, high-concept gore-fest Saw III.

Deep in the latest warren of deathtraps conceived by murderous mastermind Jigsaw, behind a door painted with the words "here's your chance," the device standing in front of us looks like a crucifix fashioned out of steel beams, clamps, cables, motors and gears. There's blood (or the special effects version thereof) pooled around the base of it, and a few chunks of disturbingly lifelike ersatz flesh.

Arms get strapped in here, feet get wedged in there, head goes inside this clamp contraption. But what are the gears for? When this thing is powered up, won't the gears just rotate the clamps in place and make the victim's ... oh. Okay. Got it.

You know the famous scene in The Exorcist, where Linda Blair's head spins a full 360 degrees? Imagine a contraption that does that to you without the benefit of satanic possession. And to your arms and legs, too, twisting them in their sockets until flesh, muscle and bone rip and snap like wet tree bark.

Jigsaw, you're a sick, sick man. But that's why moviegoers love you so.

Saw III, which wraps shooting this month at Toronto's Cinespace Film Studios, is a homecoming of sorts for the monstrously successful horror franchise.

"We shot Saw II here in Toronto, in the same studio, same crew. So by now it's like family," said Leigh Whannell, co-creator of the Saw franchise with fellow Australian filmmaker James Wan.

"It's another day at the office, breaking people's limbs off, body parts flying everywhere," Whannell said last week during an interview on set. "It's good times."

The affable Aussie's demeanor belies the unspeakable stuff going on a dozen metres away. Literally unspeakable - access to the set is strictly controlled, and no one's talking about the film's array of deathtraps and plot twists, for fear of spoiling the fun when the film hits theatres this Halloween.

Other than the clampy contraption, all we are shown are the sets for Jigsaw's creepy, mannequin-festooned lair and a decrepit meat packing facility (complete with disemboweled hogs hung from hooks) where much of the film takes place.

Then we're hurried off the set, though we can hear director Darren Lynn Bousman call "action!", followed by the high-pitched whine of a drill. And screaming. That can't be good.

This much we know about Saw III: The terminally ill Jigsaw (Tobin Bell) is determined to play one more sick game with a new group of victims. With the help of his protege (Shawnee Smith), Jigsaw has kidnapped a beautiful young doctor (Bahar Soomekh) to keep him alive while he leads a grieving father (Angus Macfadyen) into a new den of horrors.

The hero's peril is much more than physical, though. Jigsaw's chosen victims are the people responsible for death of Macfadyen's character's son. He can choose to help them escape Jigsaw's devious deathtraps, or sit by and watch them die slowly and very, very painfully.

The grisly shoot is taking an emotional toll on Macfadyen. "When you're doing these things, you think, 'Jesus, these things actually happen for real, there are people who do the most awful things to other people,' " he said.

"And you go, 'How can you do that? How does someone take someone's head and shove it into a bathtub full of feces and drown them in it?' I just don't get it."

Fans don't seem to care. The first two Saw movies were made on a combined budget of about $6 million US, and took in more than $130 million at the box office, plus tens of millions more on DVD. Bousman, who also helmed the last film, has high hopes for number three.

"I would say the most tame parts of Saw III are (equal to) the most extreme parts of Saw II," he said.

"It's going to be interesting to see if we get away with half the things we're shooting right now. I'm even offended looking at what I'm shooting at the moment."