It all started on a crowded New York City subway car, where, just above another commuter's sweaty forehead, I caught glimpse of a movie poster through the train window. The movie was called The Possession, and the poster depicted a young woman vomiting dozens of butterflies—or were they moths?—into the heavens above her. Written across the top of the poster was that vague promise so many of Hollywood's biggest films tout nowadays: "Based on a true story."

"How true can a movie that has a woman puking insects everywhere be?" I thought to myself. And so I googled the answer when I got to my office. The Possession, it turns out, professes to be inspired by the tale of a Jewish wine cabinet haunted by an evil spirit called a "dibbuk." A museum curator named Jason Haxton bought the box off eBay for $209 in 2004, saying that the main selling point was the hard-luck yarn from the box's previous owner, Kevin Mannis. Here is the "true story" behind The Possession's dibbuk box:

At the time when I bought the cabinet, I owned a small furniture refinishing business. I took the cabinet to my store, andput it in my basement workshop where I intended to refinish it and give it as a gift to my Mother. I didn't think anythingmore about it. I opened my shop for the day and went to run some errands leaving the young woman who did sales for me in charge.

After about a half-hour, I got a call on my cell phone. The call was from my salesperson. She was absolutely hysterical and screaming that someone was in my workshop breaking glass and swearing. Furthermore, the intruder had locked the iron security gates and the emergency exit and she couldn't get out. As I told her to call the police, my cell phone battery went dead. I hit speeds of 100 mph getting back to the shop. When I arrived, I found the gates locked. I went inside and found my employee on the floor in a corner of my office sobbing hysterically. I ran to the basement and went downstairs. At the bottom of the stairs, I was hit by an overpowering unmistakable odor of cat urine (there had never been any animals kept or found in my shop). The lights didn't work. As I investigated, I found that the reason the lights didn't work also explained the sounds of glass breaking. All of the light bulbs in the basement were broken. All nine incandescent bulbs had been broken in their sockets, and 10 four-foot fluorescent tubes were lying shattered on the floor. I did not find an intruder, however. I should also add that there was only one entrance to the basement. It would have been impossible for anyone to leave without meeting me head-on. I went back up to speak with my salesperson, but she had left.

She never returned to work (after having been with me for two years). She refuses to discuss the incident to this day. I never thought of relating the events of that day to anything having to do with the cabinet.

Mannis also says that his mom had a stroke near the box once, and that it made people who slept near it have nightmares. In other words, one superstitious guy making up fantasies about a piece of furniture—boxes don't give you strokes, hypertension does—is the entire foundation for The Possession's claim that it is based on a true story. If that's the case, why can't a child who believes the devil is in his closet inspire the "real-life" film Satan's Wardrobe? Can a man who believes aliens are spying on his brain lead to a movie in which aliens are actually doing that, and which is marketed as being "based on a true story"? It's someone's reality, right?

In more ways than one, this seemed like bullshit to me, so I contacted the Motion Picture Association of America (MPAA), which reviews every single piece of marketing—TV commercials, print ads, bus shelters, etc.—for every movie that goes through the Classification and Rating Administration. I asked for an explanation of what a movie must do to be able to sell itself as being based on a true story. "Is there a minimum percentage of truth that needs to be in the plot?" I asked. The MPAA's response: "The MPAA Advertising Administration does not determine whether a film is designated to be 'based on true events'—that is the purview of the producer or distributor of the film."

And there you have it. "Based on a true story" is a bogus marketing gimmick, regulated by nobody, designed to attract an audience that is increasingly obsessed with nonfictional works. That's not to say you shouldn't go see these movies and enjoy them, if that's your thing. But always go into the theater knowing that pretty much every movie you see is at least partially a lie, even documentaries.