What makes the amputation scene in "127 Hours" extraordinarily compelling is "the character is all alone and has no other way to free himself. The movie wants you in the shoes of the character it's portraying, and really draws you in," said Schlozman.
State-of-the-art special effects –the amputation scene in "127 Hours" involved several prosthetic arms full of fake blood, muscles, ligaments, nerves and bone, which Franco's character hacked his way through – also make the experience disturbingly graphic.
Other Movies That Might Make You Ill
Here are more movies possessing that rare power to totally capture viewers' minds and hearts – and wreak havoc on their bodies.
"The Blair Witch Project."
This low-budget scare-inducing flick, shot for a song, made more than a handful of viewers lose their lunch. Sure, the fear-factor was high – the movie's characters set out to document the region's legendary witch in a desolate area. When the group begins to hear and see strange things, much is left to the imagination. But the even bigger culprit was the hand-held film camera.
The jostling up-and-down motion can affect viewers, even if they're glued to their movie house seats, said Thomas A. Stoffregen, a motion sickness expert, and professor at the School of Kinesiology at the University of Minnesota.
"Even if you're sitting, your body is not entirely stationary," he said. "As you watch the on-screen images bobbing, your body is subtly swaying, and so you're not entirely in control of your neck and torso, which may lead you to become physically unstable in your seat." This phenomenon can lead to nausea, eyestrain and dizziness, he said.
An easy fix is simply closing your eyes, which eliminates the stimulus.
"Saving Private Ryan."
Few films have dared to portray war's brutality like this. On the battlefield, bodies explode, and limbs which are torn apart fly through the air. A medic's guts are graphically displayed. On seeing these types of images, explained Sheehan, the body releases certain neurotransmitters that may cause physical reactions such as nausea and vomiting, and even fainting. In addition, he said, viewers who are blocked from quickly exiting the theater may pass out.
"Any movie that deals with potential harm from supernatural forces can have a huge impact, because people can't verify that these occurrences can never happen," said Bea. The reason, he explained, is these otherworldly forces are completely unknown and, therefore, very alarming. Possible medical repercussions can include increased vigilance, and fear of being alone, especially in the dark.
"In this movie, which is filled with rapid-cut edits, the eye is getting pulled every which way," said Stoffregen. "You lose a lot of control over where your eye goes." Potential medical repercussions include eyestrain and headaches, he said, adding that, if you don't look away to stop the stimulus, you may eventually vomit.
"Interview With the Vampire."
Not for those with phobias about violence and blood, "Interview" made its gore even more twisted by having the mayhem performed by rather attractive people. "This incongruity between the handsome perpetrators and the grueling deeds can make the physical reactions even stronger," said Schlozman. Potential medical repercussions include lightheadedness, nausea and vomiting.