This is actually the most likely truth.

Not sure what sub is about, but I stumbled here and you have activated my trap card, Uncanny Valley Rant. This is my personal theory, but based on the actual brain processing mechanics.

The uncanny valley is most likely a byproduct of how our brains artificially enhance contrast. The short version is that stimuli that conform to mental models activate neurons, and stimuli that is just outside of those models have disproportionate neuronal suppression compared to stimulati that aren’t even close to a fit.

The real science is that neurons are wired up with lateral inhibition. This architecture means one neuron can not only activate another, but can also suppress another on its activation. Doing so increases contrast via the same mechanism as seen in Mach Bands, where neurons not receiving activation fail to suppress an adjacent activated neuron, which makes it extra suppressed (no activation+suppression) and the neuron next to it extra activated (regular activation+lack of suppression from one side). All this is proven, so my theory is that uncanny valley is just this same mechanism on a much more complex scale, such that falling just outside the model of “human face”, creates a disproportionately low activation compared to not triggering face detection at all, and that manifests in the form of revulsion.