Decartes, for example, did actually believe that animals don't feel or experience things, that they're purely mechanism-like entities, with simplistic (I'd even

Decartes, for example, did actually believe that animals don't feel or experience things, that they're purely mechanism-like entities, with simplistic (I'd even say, "behaviouralistic" but that'd be a bit anachronic) stimulus-response built-in reactions — they were not able to geniunely experience pain or distress, they could merely exhibit outwards signs of it, that's all. Fortunately, with computer-based AIs we know for sure that the analogical beliefs are actually true, and there are no future developments that could possibly change that.