But how terrifying is the film, really? Anyone who pays attention to ratings controversies, or who has seen Kirby Dick's excellent 2006 documentary on the MPAA, This Film is Not Yet Rated, knows that the ratings board is notoriously arbitrary and not prone to explaining their actions publicly. When Hamada says the association told the producers there was nothing that could be altered in the film to get it a PG-13, we have to take his word for it—or go see for ourselves, which is certainly what The Conjuring's producers were banking on.

But despite the narrative that has sprung out of all this, which is the sort of publicity that horror impresario William Castle would have killed for back in the '50s and '60s—"The filmed deemed too scary for teens!"—it's not like this is the first time a film has been rated R largely for the ambiguous "terror." Nor would it be the first time such a rating might be questionable.

In 1996, just before he was tapped to make the Lord of the Rings, Peter Jackson filmed his first sizably budgeted work for a major studio, the Michael J. Fox-starring horror comedy The Frighteners. Despite its light tone, a minimum of any significant scares, and the fairly cartoonish nature of the violence, it got saddled with an R rating for the same elements as The Conjuring: violence and terror. The Frighteners isn't nearly as frightening as, say, James Wan's last film, Insidious —which is cited for violence and terror in the MPAA's explanation, but also for language and disturbing images. Insidious, however, was only a PG-13.

Then there's Sam Raimi's goofy, slapstick Army of Darkness, which the MPAA seemed to really have it out for—it initially received not an R, but an NC-17, for nothing more disturbing than a zombie getting beheaded. Who knows what would happen if AMC's The Walking Dead was subject to weekly review by the board.

All of this raises a question: Just how can terror be measured? Short of hooking audience members up to an EEG and EKG and analyzing brain function and heart rate, or trying to monitor adrenaline production over the course of a movie's running time, how do you quantify the subjective quality of fear?

Here's one measure. Let me preface by saying that advance screenings of horror films are usually terrible, often having little to do with the quality of the movie itself. These promotional screenings, set up for the media to attend with a band of lucky moviegoers who've been given free passes to the early showing, highlight almost all the reasons many people hate seeing movies in the cinema. Even more than for any other genre, advance screenings of horror seem to give people license to try to prove to the world that they're not scared by yelling at the screen, laughing at wildly inappropriate times, and loudly attempting to predict to their neighbor what's going to happen next.