One of the most frightening things I've ever heard is when someone pointed out that the existence of the uncanny valley implies that at some point there was an evolutionary reason to be afraid of something that looked human but wasn't.
Well that's interesting as the good esoteric spiritual teachers (as opposed to the junky channelled nonsense ones) speak of an Atlantean civilisation where human beings had fills, but that it was an aqueous atmosphere (none of this living underwater Disney stuff).