Emotion is surely one of, if not the primary driving force behind cinema. Why do we ever sit down to watch a movie, if not in the hope of feeling something?
Obviously the emotional responses vary according to what we chose to sit down to. Sometimes we're just looking to be amused; sometimes we want to be deeply moved. Often we want excitement, be that simply in an adrenaline-pumping rollercoaster ride way, or sometimes in a more intimate manner.
However, there are also times when some of us - by no means all of us - want to really test what we're made of, and take on something that plunges us into the darker side of our emotional spectrum: fear, despair, pain.
Countless films set out to inspire such reactions; just how many really succeed is debatable. But all of us have experienced moments from cinema that have pushed us further than we might have expected; moments which, for some, may have left us asking whether the filmmakers went too far.
Here are 10 such films. All can be broadly classed as horror, yet none are content to simple scare you in the standard, jump-out-and-shout-BOO! manner. These are films that get deep under your skin, dig into subconscious anxieties you might not even have known were there.
None are best watched alone - but all definitely deserve to be seen. This can't necessarily be said of all the most notorious titles that frequently appear on the 'most disturbing movies ever' lists.
10. Henry: Portrait Of A Serial Killer
Although it didn't reach a wide audience - and with it, widespread notoriety - until the early 1990s, director John McNaughton's directorial debut was originally completed all the way back in 1986. Hard to believe, given how radically out of step it was with the predominant American horror cinema of the time.
Based loosely on the real-life crimes of Henry Lee Lucas and Otis Toole, Henry: Portrait of a Serial Killer stars Michael Rooker (making his film debut) as an anonymous working class resident of Chicago, who commits an ongoing series of random murders, and introduces his roommate (Tom Towles) to the horrific pastime.
The film met many problems with the censors, particularly in the UK when, for a time, it was only available in a cut which not only excised certain offending moments, but actually re-edited one specific sequence to make it less harrowing. (The BBFC finally passed it uncut in 2003.)
Shot on grainy 16mm film, the low production values and stark city streets lend the film a sense of kitchen sink realism, which is key to its success. Rooker's inherent charm as an actor, and the script's hints toward some vague underlying morality within Henry, only serve to make him more terrifying.
All of which makes it strange to think that today Rooker is beloved by young and old alike for his role in the Guardians of the Galaxy movies.