To those who have seen the film...*SPOILERS*

Since your question has sat here for five days without a reply, I figured I'd answer it even though I haven't seen the movie, but instead have read a review that discussed the pivotal scene.

The review says that, when the main characters are camping at one point, two men with AK-47s enter their camp and one of them points his rifle at them. The male protagonist, getting in touch with his inner George Costanza, shoves his fiance/girlfriend in front of himself to use as a human shield. However, he quickly realizes how bad that maneuver was, and presses his head against the barrel of the gun to make up for it. The guys let them live and one of them gives the male protagonist dark sunglasses, almost as a hint that he's going to live his life in shame after what he did.

The gun was intentionally aimed at her forehead, not his, it's not his fault the gun was intentionally aimed at her foreheadHe was partially behind her when the gun was aimed at her foreheadTo stand fully erect to "stand his ground" he had two choices: slightly slide behind her or push her to the side altogether; pushing her to the side is Action which might have triggered the gunman to shootHe slid fully behind her with his hands firmly on her shoulders, as if she was a child, and a female child to boot, that he was offering up for a sacrifice, but the maneuveur was was subtle challenge to the farmer with the gun: gunman, would you dare shoot a woman, especially a woman who physically appears to be childlike?What he did was much more complicated then merely using her as a human shield: standing behind her with his hands firmly on her shoulders was in itself an act of defiance (would you dare to shoot a woman/child) and that act of defiance was his weaponShe was the coward from beginning to end because she played the role of weak child martyr who needed taking care of while at the same trying to prove that the contradiction of her age versus her childlike physique was proof of her worldly experienceHe took care of her from beginning to end, even during that brief second when he offered her up as a sacrifice because the act of offering her up was an act of defiance and a challenge to the gunmanAfter that key scene is another key scene, the crossing of a riverlet, which I feel is the true pivotal scene because it's a scene in which Bernal's character keeps his back turned on her when she's about to cross a riverlet, he refuses to babytalk her through the simple crossing, he intentionally keeps his back turned on her knowing she'll fall (because she can't do anything with a hint of risque unless somebody holds her hand, she can't even remove a mote from her eye, it takes Bernal and the guide to remove the mote....... ) and predictably she falls in and predictably she wails and cries like a child and refuses to get up and wade across the river like an adult.....The coward is the woman because she expected everybody to do everything for her, and even after the fall in the river - her life flashing before her eyes for a second time, the fall in the water a metaphor for purification/rebirth/baptism - she failed to grow up and learn her lesson and feigned naivety, there was no rebirth or redemption for her, not even when she spurned the guide because she opened the door for the guide to make a pass at her, she pretended to be surprised he took the bait and pretended to act surprised when he kissed her on the mouth then launched into yet another temper tantrum after she not only allowed him to kiss her but kissed him back.She (the character) was a piece of work, the actress who played her was phenomenal and should have been nominated for an Oscar for Best Lead Actress