The litmus test of a giant killer-snake movie is whether or not the thing is scary, and director Luis Llosa delivers a plausibly thrilling ride, relying heavily on the horror conventions codified by JAWS. It won't take viewers long to realize that the callow, youthful documentarians led by cocksure anthropologist Steven Cale (Eric Stoltz) and first-time director Terri Flores (Jennifer Lopez) are going to be tested by the Amazon in their quest to find and film the anaconda-worshiping Shirishama Indians. The film's foreboding atmosphere is so efficiently established from the outset (cinematographer Bill Butler also shot JAWS) that when the crew comes across stranded snake hunter Paul Sarone (Jon Voight) -- whom their enigmatic, Brazilian riverboat captain Mateo (Vincent Castellanos) already seems to know -- you know there's bad trouble ahead. The ruthless and opportunistic Sarone promises to guide them to the lost tribe, but instead takes them on a perilous hunt for the killer anaconda. Voight's performance -- one of the film's pure, trashy delights -- is all leer, sneer and macho swagger, while the rest of the actors feel like the disposable snake-fodder they are. The animatronic snake is generally a nicely nasty piece of work, but can hardly live up to the revolting title card that tells us just how it kills its victims: First it crushes their bones and swallows them whole, then partially digests them and regurgitates them before finally finishing the job. Consider that on the way to the concession stand.