[pbhjpbhj]

A 10-week fetus, ie 20 weeks of gestation, can hear [1], suck, swallow. I would not say it's obvious they can't experience "mental states"; especially not as you appear to be arguing almost all animalkind can experience those states.

[1] https://medlineplus.gov/ency/article/002398.htm

[nihilismislove]

Well, that wasn't my main point and I did mean 10 weeks of gestation (just as an example).

Still, physiological responses are not the best indicator of mental states - plants and primitive animals (from sponges to bivalves) have them too, despite lacking the neurological development necessary for (or evolutionary need for) "consciousness".

[pbhjpbhj]

Your second paragraph there seems to refute your position. If you can't tell physiologically then how are you telling that "most vertebrates experience mental states". You seem to be arguing for an assumed position starting from that position (petitio principii).

And I agree that physiological responses aren't the best way to show mental states. I cry sometimes for no reason whatsoever, my eyes just leak; you can't infer fear just because a creature backs away from fire, either.