Can you explain the uncanny valley and what that means for vampires?
Uncanny valley is when something, like a robot, an artpiece, or an animated character, looks human. Except it... doesn't. We can tell that we're not looking at a real human, but we can't tell what it is that gives it away.
You can't put your finger on it, but you know instinctively, that you're not looking at a human being. It creates a sense of discomfort.
That's the uncanny valley.
It's a term coined for robots, and used in design. Basically, you don't want your robots looking too humany. Make them look like seals or cats or whatever, give them outlandish features, just make sure you're not giving them too human features because then your clientele will shake their heads and say "Oh. Oh, I don't like that. Nu uh."
As for what causes uncanny valley, there are many theories. Some say that it's from when homo sapiens had competitive humanoid species, and we had to tell our own species apart from others. Except, we bred with these other species, so I personally am not too swayed by that one.
Another theory is that it's to help us recognize threats. People with rabies look distinctly wrong, their movements very off.
The point is your brain says "nope".
This, for the record is why the Sims still look distinctly cartoonish. It's not because the devs can't make them look more human, it's that they don't want to because that would be terrifying and no one would by their games.
One example, perhaps a bit silly, of this is Baby Yoda. I'm not sure how good an example this is since it appears to be just me, but I get the creeps from that baby. He's designed to be as cute as possible, and I think that's what makes him so off-putting, because I find him terrifying. His eyes are too big, black, and empty, and he's too inhuman. He looks like he's going to lure me in, like one of those fish or insects you hear about that mimic their prey's food source, and once I'm close enough I'm dinner. It's that "I can't trust this creature" feeling. I never ever want to see Baby Yoda merch in real life.
A better example provided by @theoriginalcarnivorousmuffin:
From Battlegirl Alita live action. You know at a glance she's not human.
As for Twilight vampires, they're too symmetric and beautiful, their skin isn't human skin, their eyes are the wrong color, sometimes they forget to move right. Uncanny valley galore.