Whether it's a Lovecraftian cosmic entity that's unknowable in size and scope, or a simple jump scare designed to catch us off guard, horror is at its most brilliant when it's toying with the concept of the unknown. And that works for whatever film genre we're talking about; throwing in something that doesn't fit its surroundings as a narrative left turn only serves to make it stand out, and stress us out, that much more.
Even when we're coming prepared to a movie we know is going to be dishing out perturbing content, the very best films are the ones that ratchet it up ten levels when you least expect it. The ones that leave you reeling in the aftermath. The ones that make you double take and question 'what on earth was THAT?!'
So then, these are the movies that used horror as a weapon, attacking both our senses and sensibilities with deviations into the horrifying when we're nowhere near prepared to deal with it. From sweet, beautiful love stories twisted by arresting imagery, to genre fare that subverted expectations to jaw-dropping effect, these are the moments of horror that make their movies all the more disturbing.