That "pseudo-human laughter" gave me some real chills; didn't realize uncanny valley for audio is a real thing but damn...

I use regularly AI music services to build rock songs out of my lyrics, old poetry or popular songs, etc. and sometimes they hallucinate in creepy ways, adding after the song ends either evil laughter or horror sounds, demon-like voices, starting singing in completely made up languages. They're creepy but fun and interesting at the same time. Creepy sounds aside, I've had a lot of fun experimenting with AI music hallucinations as they sometimes create interesting and unusual things that spark more creativity (I'm already a musician); I sometimes felt like someone who grew up listening only bad pop trash being suddenly exposed to Frank Zappa.

Sometimes when I lie awake at night I wonder what it is about things that are "almost human" that terrifies so many of us so deeply.

It's like the markings on the back of tiger's heads that simulate eyes to prevent predators from attacking it. I'm sure there used to be something that tigers benefited from having this defense for enough for it to survive encoding into their DNA, right?

So, what was it that encoded this fear response into us?

Dead things, and behaviors that don't align with our predictive models shift the context to one of threat - if something shaped like something you understand starts behaving in a way that you no longer understand, you'll become progressively more concerned. If a pencil started rolling around aggressively chasing you, it'd evoke fear, even though you'd probably defend yourself fairly capably.

If enough predictive models are broken, people feel like they've gone crazy - various drugs and experiments demonstrate a lot of these factors.

The interesting thing about uncanny valley is that the stimuli are on a threshold, and humans are really good at picking up tiny violations of those expectations, which translates to unease or fear.

Other hominids as well as visibly diseased humans.

Corpses. Bodies not dressed as deceased imply existence of a threat.