Full disclosure: I borrowed this one from Kurt Vonnegut's preface to Bagombo Snuff Box, what he called "Creative Writing 101," but this particular tip, which reads in its entirety, "Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them - in order that the reader may see what they are made of," (1 of 8) applies to this film wonderfully. There might be other movies more brutal on its main characters (I'm looking at you, Hostel...), but what this movie does more than most is start your characters in one place, then leave them somewhere entirely different. At its most basic, this is simply good storytelling. If a lot of these other elements are already engaged in your story, this tip should simply fall in to place. Consider the first 10 pages and Roger Ebert's assessment of a narrative out of control in the best possible way. Charlie, our naive, Corporate Vice President, leaves his safe office and encounters a force of nature. But one thing Frye does in his writing of the story, is that he lets the tone dictate the type of tests for the characters. At first, it's as simple as the way Charlie grips to the car, terrified by Lulu's driving - but after the tonal shift at the mid-point (another element already inherently established in the narrative), the tests get darker, and far more dangerous.