People have passed out. People have thrown up. Some have even reportedly gone into seizure.
The gruesomeness of 127 Hours, a new movie that tells the story of real-life mountain climber Aron Ralston, who was forced to cut off his own arm after it was trapped by a boulder for nearly five days in Utah in 2003, has triggered a range of visceral responses among audiences. But is it all just a clever marketing ploy, or can watching a movie really cause these types of reactions?
It can and it can't.
"With various types of noxious stimuli, often painful or even emotional, it affects people's vascular reflexes ... and often either that makes your heart race, because you're scared and it's a fight-or-flight response, or sometimes, paradoxically, it can make your heart kind of slow down," says Peter Tai, a neurologist at the Krembil Neuroscience Centre, part of the University Health Network in Toronto.
It's typically the latter in situations like this, Dr. Tai says. "Your heart slows down, your blood pressure drops, and it's not enough blood pressure to support your level of consciousness. You end up passing out."
Medical experts don't know exactly why some people's blood pressure drops when they are exposed to stimuli like watching a man amputate his own arm, even if it is on film, Dr. Tai says.
"We just know that there are certain people who are quite sensitive to noxious stimuli like that. More often you hear about it in kids who don't like needles and faint every time they see a needle or every time someone actually sticks them with a needle," he says.
That may be the typical example, but "it really can be anything," whether it's someone becoming faint at the sight of blood or hitting your funny bone, Dr. Tai says.
The phenomenon, known as vasovagal syncope, can also cause vomiting because the parasympathetic nervous system, which slows down the heart rate and drops your blood pressure, "also has some controls on the stomach," Dr. Tai says.
Although 127 Hours doesn't hit theatres until Friday, reports from early screenings have been rife with people reacting to the film, including three who fainted during a screening at this year's Toronto International Film Festival.
A survey on Movieline provides gives the tally to date: at least 13 faintings, one panic attack, two instances of light-headedness and three seizures.
James Franco, who plays the mountain climber, gave an interview during TIFF in which he said he watched the videos Mr. Ralston took before he made his fateful decision to save himself. "When you see him in those videos, when he had no idea if he was going to get out ... it was just extremely powerful," Mr. Franco said. "Here is this guy accepting his own death, but not wallowing in self-pity or anything."
But in all likelihood, no one has really gone into seizure watching 127 Hours, Dr. Tai says.
"The convulsion that occurs in association with [vasovagal syncope]comes from people not realizing that it's a fainting spell and from keeping their head up," he says.
"What should happen when someone faints like that is you should lie them down on the floor so there's the least amount of obstruction to blood flow to the brain. That will allow them to regain consciousness as quickly as possible.
"Where people kind of have convulsive activity when they faint like that," he adds, "it's because bystanders unwittingly make it worse by trying to prop the patient up. That just means their blood pressure doesn't really have a chance to recover, and so their brains kind of throw off a few convulsive movements. That's not a seizure."
Such convulsive movements are "not uncommon," Dr. Tai adds.
Buy your ticket with caution.
Reelly gross
It may be the latest instance of shocking cinema, but 127 Hours is not the only movie that has seen audiences barfing, fainting or running for the doors.
The Passion of the Christ
One woman suffered a fatal heart attack while watching the film's crucifixion scene.
Antichrist
Lars von Trier's film prompted vomiting at the Toronto International Film Festival last year, and also reports of seizures among audiences in New York.
The Exorcist
When William Friedkin's horror classic hit theatres in 1973, it was so shocking that people reportedly vomited, fainted and ran from the theatres, although many such instances were later said to be publicity stunts.
The Blair Witch Project
Wobbly camera work in the low-budget horror film was disorienting enough to cause some audience members to throw up.