The 1932 original Freaks.
Would the Theatrical Performance bring people into the scene, or relax the audience because they know the story is confined to the limits of the stage? I don’t know, but it could be performed with no adaptation. Certainly more than something like Speed.
Hell, it freaked me out three weeks ago when I watched it and I’m in my 60s. 
It’s the lighting; very effective. Plus, the witch is just so ugly!
I liked it, but the book was better and scarier.
My nom is Cat People. All mood and suggestion.
I also like The Haunting a lot. I’ve seen it at least five times, and it never fails to get me. I like The Turn of the Screw, too.
I watched this the first time thinking not a lot of thought went into it. After it was over, I learned that a great deal of thought went into it. But I really couldn’t tell that by watching it. Maybe it rewards rewatching, but I had a bit of trouble with it because the characters are all People You Hate At Every Dinner Party.
If you had to pick one low-budget sci-fi movie, make it Primer, which manages to be entertaining while also totally incoherent.
I don’t remember much gore in The Thing but it scared the shit out of me as a teen. Kurt Russel version, obviously.
Are you joking?
That movie is so gory, it’s fascinating.
From a certain perspective, Into the Woods is a horror story. Try to watch the Broadway version rather than the 2014 movie.
It’s been a looong time.
A lot of people at the time felt as though The Thing was unnecessarily gory. Roger Ebert referred to it as a “great barf-bag movie.”
It’s -quite- gory, but a wonderful movie. So now @tride has the most excellent of homework assignments in having to go watch it again…
You may need a nightlight for a few days.
And may look askance at your pets. And friends. And anyone else…
Yeah, seconded. Great movie. I think the effects hold up pretty well, too.
I’m really not kidding when I say ''fascinating" gore. It takes traditional ideas of gore and combines it with body horror in a way that you’re kind of detached from the whole experience because you’re just trying to figure out how the Thing works. At least that was my experience both times I saw it (decades after it was released.)
Nosferatu, 1922. At least, I don’t remember it as being gory.
I love that movie! Even the first time when I had no idea what was going on.
An obvious one that just occurred to me:
Willy Wonka and the Chocolate Factory
Godzilla : Minus One.
Would Saltburn qualify? A little blood, but no gore, and it does have a monster.
I could be wrong, but I always thought this was based on DMFM (AKA Dial M For Murder), not Strangers on a Train. Both Hitchcock movies, but very different.
it’s both; the scene where she fights off the thug & scissors him to death is from Dial M, but Michael Douglas blackmailing Viggo to whack her is almost like SOAT, in which 1 guy goes ahead 1st boxing the 2nd guy in.
As a youngster, The Watcher in the Woods from 1980 really scared me. I’m not sure why, or even if it would count as a horror movie. There’s also Return to Oz.