"The severed body didn't fall to the floor with exactly the right trajectory, plus the director really wanted the actor's eyes open during the decapitation," recalls Jon Campfens of a scene in Saw V, fifth in the gloriously grisly horror series from Lion's Gate Films that opened to blockbuster business last week. Campfens' company, Switch VFX in Toronto has supervised visual effects on the last three Saw features.

Close Move

"The severed head didn't fall to the floor with exactly the right trajectory," says Saw V visual effects supervisor, Jon Campfens. Read about how Jon and his team augmented this scene and get the inside scoop on other Saw series' secrets. Clip courtesy of Lion's Gate Films and Switch VFX. (Click to play. Movie will begin playing once loaded.)

For those who haven't, well, seen Saw, the series revolves around the Jigsaw Killer who kidnaps a series of victims (usually pitted against each other) and places them in deadly Rube Goldbergian traps that afford them the opportunity to repent the ways in which they may have taken their wonderful lives—or the lives of loved ones—for granted, or suffer the consequences.

Saw Series Superstar: The Jigsaw Killer. Image courtesy of Lion's Gate Films.

In the first Saw, for instance, a doctor has to saw off his own foot and leave his fellow victim—chained to a rusty, old industrial wash basin—for dead in order to save his own skin. And though the series has tried to remain true to its gritty, low-budget roots (the first movie cost $1.2 million and grossed over $100 million worldwide), the visual effects have gotten more complex with each installment.

Head First

"Going into prep; we knew we had the decapitation to look forward to," jokes Jon. "Head comes off, body drops. Usually, we'd shoot that kind of thing against a green screen. But after seeing the trap, we knew there was no way to shoot the element, or actor, somewhere else, then bring back the trap in post. Everything would require rotoscoping."

Rotoscoping refers to the technique of matting, or separating, an "element"— an actor, prop or set piece—from a live-action "plate," or footage, so it can be composited, or digitally "blended," over another background later, in post-production.

The live-action plates didn't align exactly for this gruesome decapitation sequence in Saw V. Image courtesy of Lion's Gate Films and Switch VFX.

In the scene, five victims linked by a rotten real estate deal (hey, someone's gotta pay for the sub-prime mortgage mess) are tethered together via wire threaded through collars around their necks, and they're cuffed to guillotines timed to decapitate them. The "gag," as its known in Saw parlance, is that the keys to each collar lay tantalizingly out of reach in five glass cases. If the victims can work together to retrieve the keys, they'll escape. If not, at least one will go all Marie Antoinette on the audience.

Talk about a severance package! Image courtesy of Lion's Gate Films and Switch VFX.

"We shot a live-action plate of the actor yanked back into a cage without the guillotine," Jon explains, "and then shot the plate again with a sock around the actor's head to contain her hair and simulate the severed body falling forward." When the team got into post, though, there were problems with the plates, which didn't align properly. "We had to fix the alignment in post, and resize her body so that all the elements fit together," says Jon.

"The actor's eyes were closed during the part of the scene that was supposed to simulate the decapitation and the director wanted them open," recounts Campfens, "so we added open eyes from a different plate, which made the shot much more horrific. We had to create a computer-generated head, a CG 'dog collar,' and lots of digital blood." Now, a CG head typically requires a full, 360-degree laser scan of the actor, but, since the budget didn't allow for a fully-scanned digital double, Jon created his "poor man's" version through a series of hi-resolution still shots (10 megapixels) of the actor rotated through the same angles.

There Will Be Blood

"Budget constraints do force us to get creative," says Jon. Since VFX is his stock in trade, it might be surprising to know that Jon also likes his "elements" as real as possible—including blood. "Well, despite what you might think, we don't engage in ritual sacrifice around here," Jon laughs, "so, when I say 'real blood,' I mean shooting that element in-camera using practical effects like liquid corn syrup dyed red, which the crew shoots seven ways to Sunday." And still, they'll need to augment it. Like every other liquid, blood is tricky to render digitally. "There's a viscosity to it," says Jon, "and a way that light plays on its surface."

Sweet treat: That dripping blood (liquid corn syrup dyed red) began as a practical, in-camera effect before being enhanced in post-production. Image courtesy of Lion's Gate Films and Switch VFX.

Light and reflection are particularly difficult to render on shiny, hard-surface 3D objects like the pendulum in one scene that swings down and slices its victim open with the precision of a Ginsu knife. The resulting "object" is a combination of practical and virtual (the CG pendulum was created with Maya). Jon says working on these scenes is a lot of fun. In fact, he says co-worker Gudrun Heinze, a compositor he describes as a "gentle, animal-loving vegan" gets the most perverse pleasure out of doing "virtual harm." Better that than the real thing.

Close Move

Ever feel like the walls are closing in on you? The protruding bone is entirely virtual. Clip courtesy of Lion's Gate Films and Switch VFX. (Click to play. Movie will begin playing once loaded.)

Campfens and his band of merry mayhem-makers eagerly anticipate work on Saw VI, slated for an October 2009 release. After all, like the Macy's Thanksgiving Day Parade and a visit from Santa, the Saw films have become a holiday tradition.