AFTER wading through the entrails of Captivity, Hostel: Part II and Vacancy, the wanton carnage of the fourth Saw picture lacks some of the shock value of previous films.

Hyperactive editing doesn't help, rendering a couple of the elaborate death sequences an incomprehensible blur, and characters are sketched in such flimsy detail that their grisly demise doesn't matter a jot.

At least one potential victim could be saved from her horrific fate by simply pulling a trigger.

Instead, her would-be saviour wastes valuable seconds searching for a more complex solution, affording Francois Dagenais and his prosthetic make-up team plenty of time to create gory images of skin being ripped from the bone.

Saw IV opens with the stomach churning post mortem of evil and twisted Jigsaw (Tobin Bell), the deranged puppet master unable to escape the spectre of cancer.

Detective Hoffman (Costas Mandylor) arrives to take charge of evidence retrieved from the arch-villain's innards.

He is joined by two tenacious FBI profilers, agents Strahm (Scott Patterson) and Perez (Athena Karkanis), who offer to help piece together the evidence and reveal Jigsaw's twisted genius.

The stakes are raised when SWAT Commander Rigg (Lyriq Bent) is abducted from his home and thrust into a maze of fiendish traps, with just 90 minutes to save his life.

The cops race against time to save their compatriot and expose the madman's diabolical grand scheme. They hope Jigsaw's ex-wife Jill holds the key to unlocking the killer's secrets.

Saw IV criss-crosses narrative threads from the previous films, reintroducing at least one familiar face and embellishing the complex back-story of Jigsaw aka John Kramer.

Scriptwriters Patrick Melton and Marcus Dunstan try to paint their demonic murderer as a victim himself, but four films (thus far) of gruesome survival games seems like overkill to justify one man's grief and disillusionment.

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