The disintegrations of the couples' relationships parallel their turns to brutality. Their fights and frustrations lead directly to ugly violence. Jeff, an aspiring doctor, diagnoses injuries, decides on "treatments" ("Keep his legs clean," he says of a comrade with a broken back and gashed legs), and protests their situation ("This doesn't happen," Jeff blusters, "Four Americans on vacation don't just disappear"). While the others are less convinced that someone will come save them, they do go along with his decision to amputate the legs of the comrade with the broken back. This leads to excruciating pain and gruesome imagery, as they break the legs with a rock and cut them with a hunting knife.
In another sequence, when one girl believes the vines are inside her body, she begs Jeff to cut them out. Though he agrees to a couple of efforts -- horrified as he pulls out the long, green, trembling cables -- at last he has to stop. "There's no more cutting," he says flatly, "We can't keep cutting." In this, the film achieves something like a metaphor, as the tourists' fears have infected their very beings, vine-like, and their decisions are increasingly ineffective precisely because they're based on fear and ignorance.