I doubt there's any objective definition of pain if you simply assume the subject in question isn't a reliable narrator (they could be a p-zombie, or faking it, or it could be entirely programmed behavior...), so yeah, at some point you have to go with the affect -- they look like they're in pain, they act like they're in pain, and sure, my judgement of that is biased by my own perspective as a human with certain brainbits that make that call, but they're making that call and that's got a direct impact on my own perceptions of the situation.

I often sympathize with machines and objects as well, BTW. >> But I'm like that.