There's an unspoken agreement between moviegoers and filmmakers who make safe, mainstream fare: If the former gives the latter's work a look, the latter won't do anything to disrupt the viewers' emotions beyond the norm. There may be some laughs, some jolts, and possibly a tear or two, but nothing that will leave any permanent scars.
Then there are those directors who don't care about that agreement. They want to leave marks.
It's those moments in a movie where people either cover their eyes, peek through open fingers to catch a cautious glimpse, or stare at the screen in disbelief, as if a freight train is pushing toward them and they're frozen in fear. It can be a scene marked by such intense violence that it's nauseating, a conversation so uncomfortable you can't handle the second-hand embarrassment, or some other heinous exhibitions of mankind's darkest impulses.
Whatever the case, they don't get much more aggressive than what's seen in the 50 most hard-to-watch scenes in movie history. Consider this the all-encompassing cousin of last month's collection of traumatic dog death scenes.