Warning: This post contains spoilers for Drag Me to Hell.
So, here's the theory: What if Drag Me to Hell were one of those movies, like The Innocents (or, according to some viewers, Mulholland Drive), that contain two separate possible readings, one supernatural and one not? On the first level, it's just what it appears to be: the story of a girl who denies an old woman a bank loan, falls under a Gypsy curse, struggles desperately to change her fate, and is eventually (I told you there'd be spoilers) dragged down to hell. (God, that ending! With the title of the movie flashing up in bold right after, just to drive home the point!)
But in the second reading, the viewer is seeing the world as skewed by the vision of a mentally disturbed young woman; what appears to be a chain of fated supernatural events is nothing more than the sum of Christine's paranoid visions as she slowly loses her mind. Yes, she really does deny Mrs. Ganush the mortgage extension, and they do have that fight in the parked car in the parking lot, after which the old woman curses her. (In the alternate reading, there may be no true supernatural events, but the Gypsy still believes there are or, at least, knows how to prey on Christine's weakness.) But everything that comes after—the meetings with the Indian psychic, the visitations of the lamia to her house, the séance with the medium—is either a figment of Christine's imagination, the work of unscrupulous shysters out to exploit her, or a combination of both. (By sheer bad luck, two of these shysters—the old Gypsy herself and the medium Christine hires to exorcise the demon—die in the process, compounding both Christine's guilt and her sense that something evil truly must be afoot.)
In the final scene, when her boyfriend brandishes the evil button and asks where his liberty quarter went, Christine simply backs onto the railroad tracks out of fear. She gets run over by a train, yes, but the image of Hell opening up to drag her into its burning maw is merely the dying vision of a woman who's now gone definitively mad. All Justin Long sees is his girlfriend getting crushed by a train, which would certainly be horrifying enough to justify his reaction.
The funnest part about this girl-gone-mad theory is that you can go back through the movie and apply it scene by scene with psychoanalytic rigor. The moment where she projectile-bleeds onto her boss? An ordinary nosebleed, blown out of proportion by her fevered mind (not to mention her barely repressed hatred of said boss). But the nonsupernatural reading has its tragic side as well. If Christine never really did face the threat of eternal punishment, then that kitten was sacrificed for nothing at all.