Squeaky-clean honeymooners Steve Zahn and Milla Jovovich go backpacking on a remote Hawaiian island but find themselves sharing the trail with two other couples. Steering clear of the first (Chris Hemsworth and Marley Shelton), who have “redneck psychopath” tattooed on their foreheads, they team up with the second (Timothy Olyphant and Kiele Sanchez), then develop serious reservations about them too, what with the metal plate in Olyphant’s head and the commando knife strapped to his ankle. Writer-director David Twohy (Pitch Black) serves up mechanical thrills culminating in a bogus twist ending. R, 97 min.