At its best (or worst, depending on your perspective), horror taps into our most basic, most elemental, and most primal of fears. No fear is more basic, more elemental, or more primal than fear of the dark. As our ancient ancestors learned, what you don't see can most certainly, definitively cause you grievous bodily harm, up to and including dismemberment and/or a painful, excruciating death. Add to that primal fear of the dark a labyrinthine cave system, lost spelunkers, and cannibalistic mutants and you get something like Neil Marshall's ('Centurion,' 'Doomsday,' 'Dog Soldiers') second (and, so far, best) film, 'The Descent.' Released in the UK and Europe in 2005, but not released stateside until the following summer (with an alternate ending no less), 'The Descent' is survival horror at its most compelling (and terrifying, of course).
Like Steven Spielberg three decades earlier with 'Jaws,' Marshall smartly saved the big reveal, the mutants who pose said grievous threat to the lost spelunkers at the center of 'The Decent,' until close to the halfway mark. Marshall instead focuses on the spelunkers, Sarah (Shauna Macdonald), Juno (Natalie Jackson Mendoza), Beth (Alex Reid), Rebecca (Saskia Mulder), Sam (MyAnna Buring), and Holly (Nora-Jane Noone). Onetime best friends and extreme sports enthusiasts, Sarah and Juno's friendship has frayed since the death of Sarah's husband and daughter in a car accident. Juno hopes spending their vacation exploring caves in the Appalachian Mountains will help repair their relationship. She's wrong, of course.
What's meant as a friendship-strengthening exercise, however, quickly devolves into survival horror. Mistakes - some minor, some major - along with Juno's decision (made without the participation of the others) to explore a different set of caves, spells the group's potential doom. Sarah isn't blameless, either. Her initial inaction, her initial passivity allows Juno to become the group's leader. When a rock-fall blocks their way out, the group has only one alternative: down into the unlit unknown, with only their dim flashlights to light the way. One character slips and breaks a leg, raising one question (i.e., how to get her out without slowing the group down), while also making them more vulnerable to the mutant monsters (called "crawlers" in the end credits) that have made the underground caverns their home.
That's all slow-burn set-up for 'The Descent's' breakneck second half. One woman thinks she sees something drinking water at an underground pool, but her story's dismissed as a hallucination until, that is, the crawlers make their presence known; attacking the group, targeting the weakest members of the group as predators typically do before hunting down the remaining spelunkers.
The crawlers have all the advantages: A) They're intimately familiar with the underground cave system (it's their home, after all), and B) they've developed night vision under the evolutionary pressure of total darkness. The women, divided by their individual responses and Sarah and Juno's conflict, really don't stand a chance, but that doesn't stop us from rooting for them to survive, even as we know most, if not all, won't.
That first time the crawlers attack, shot in near virtual darkness with the exception of the women's flashlights, may be a jump scare in the classic sense of the term, but it's a jump scare that's more than earned by the preceding forty odd minutes. Marshall carefully delineates the characters, especially Sarah and Juno, their personalities, their relationships and underlying tensions, before sending them down into the labyrinthine cave system (being lost adds yet another layer of fear). It's that steady build-up and the drip, drip, drip of water on the cave's walls that effectively primes the audience for the nightmare to come. Then Marshall makes us wait, increasing the combination of dread and anticipation horror fans know all too well before finally delivering the first sight of the crawler.