United 93 AAAH! Terrorists! Well, at least they aren’t snakes.

"It's a really weird day, actually. I just saw United 93, that 9/11 movie, and it's truly fucked my day up."

I was standing in line at Trader Joe's, where the cashier had asked how my day was. My response, though, was an odd understatement. In nearly 30 years of watching movies, I've left theaters with all sorts of different emotions, including desperate nihilism, but I never felt so truly damaged and shaken by a film as when I watched this verité, fly-on-the-wall re-creation of one of the worst days of my life. "Traumatic" sounds like a shrill adjective, but it's the closest word for the emotional and psychic wound gouging that I had just sat through. In an attempt to untangle my reactions to United 93, I tried to explain how terrible the experience of watching this movie was.

"Wow," the cashier said sincerely, bagging my groceries. "I'm going to have to check that out."

This weekend, millions of Americans will undoubtedly have the same reaction to United 93 as this Trader Joe's employee. Director Paul Greengrass (The Bourne Supremacy) has created (and will get wildly rich from) a movie about "let's roll." United 93 divides its time between the September 11 flight that crashed near Shanksville, PA, and air traffic control rooms in New York and Boston, where workers fought to understand what was unfolding that morning, got most of their information from CNN, and were unable to communicate with the military. Shot with a handheld immediacy and starring an ensemble cast of unknown actors, United 93 succeeds at every goal that Greengrass set out to accomplish.

If every work of art is an emotional manipulation (one that we invite in willingly, hoping to be changed for the better, to have our view of life expanded, or to have our imagination stretched), then United 93 is the dirty player at the party—the one who forgoes the rules of engagement, courtesy, or boundaries. Imagine sitting around with a group of friends telling stories about weird, true-life events. Suddenly, one person pipes up, and publicly, graphically, and extensively metes out the details of your sister being raped, or of your favorite pet getting killed. The story, excruciatingly long and expertly told, is comprised of nothing but details and tears. No redemption—no point at all, except to make you nauseous with the pain of memory. The storyteller has forsaken all social courtesies and human decencies in order to demonstrate that he tells stories more effectively than everyone else. Then he pauses to ask, "Wasn't that cathartic?"

Does it matter that the storyteller (in this case, Greengrass) is a master at his craft? United 93 would be a cinch to dismiss if it weren't so effectively made. Do we care that he doesn't offer anything but expository action? Greengrass doesn't have any thesis or point he's trying to make, besides "Watch this. Don't look away. Don't blink." No theories or conjectures are offered, and the film sticks to the nightly news version of the story. Despite all empirical evidence to the contrary, the Americans in United 93 succeed in breaching the cockpit door, where they essentially wrestle the plane to the ground. And what about the widely held theory that the plane was shot down over Pennsylvania before it could reach the White House? Boy, have you got the wrong movie if you're looking for that sort of story.

The biggest question, though, is this: Why do we collectively invite this storyteller to our homes? Why will this Trader Joe's cashier join millions of Americans in willfully reliving that incomprehensibly nightmarish morning? I have only lame theories, but no answers. And I really hope, for your own sake, that you don't invite Greengrass to tell you his story; while his re-creation is certainly effective and traumatic, the original event should be fresh and terrifying enough to last a lifetime.