Well, lighting defines a little this scene: It's something like: "I'm gonna fall in a very dark place. My only chance is grabbin' this rock and hang 'til someone gets here to save my soul."
If u take a look, There's one spot light in this scene (but it is an area light) , that means: "This enlighted rock is my only chance of survival, so I'll grab it. And if I fall in the dark area, I'll have no chances of gettin' outta there." It was the idea since the begginin'.