Ever since Open Water scared the cynicism out of the Sundance crowd in January, experts predicted the indie shark flick would take a Blair Witch bite out of the box office when it hit theaters. That time is now. Open Water was shot on the cheap ($130,000) minus the safety net of . Writer-director-editor Chris Kentis and his producer wife, Laura Lau, couldn't afford to build animatronic sharks, like Steven Spielberg did in Jaws. They had to use the real things. They took their two leads, Blanchard Ryan and Daniel Travis — playing a yuppie couple whose scuba-diving vacation becomes a nightmare — to the Bahamas, threw them in the ocean with a thin sheet of metal mesh to wear under their wet suits (can you see Brad Pitt and Jennifer Aniston doing that?), told shark wranglers to throw bait in the water to stir up the fish, turned on the digital camera and called for "Action!"p>hey got it. Open Water is open season on an audience's nerves. As in the best scare flicks, what eats at you most is what you don't see. Susan (Ryan) and Daniel (Travis) go diving, get left behind by their tour boat (it happened to a couple off Australia's Great Barrier Reef in 1998) and end up bitching, blubbering and finally clinging to each other as the fins t circling. Ryan and Travis work wonders at building characters out of the rawest materials. But from the first bite — on Susan's leg (ouch!) — Kentis never lets up on the tension. You can feel the water, stretching against an unsheltering sky, seep into your bones. The ending — a more devastating surprise than The Village could manage — caps eighty sweat-job minutes of imaginative, jolting suspense.