For the record, the chicken that survived had retained most of the brainstem. He was able to walk ("clumsily') and attempted some reflexive behaviors, but he was hardly "functional" to anyone who knows enough about chickens to assume that they do more than walk and occasionally lunge at the ground.

The chicken's ability to survive with only the brain stem isn't shocking. Anencephalic babies can sometimes breathe, eat, cry, and reflexively "respond" to external stimuli. One survived for two and a half years. This was a rare case, but so was the chicken - there were other attempts to keep decapitated chickens alive, and none have been successful.

This isn't to say that we don't have a tendency to anthropomorphize animals or treat reflexive behaviors as meaningful - we do. But pointing that out isn't where the conversation ends. Chickens are an easy target because common knowledge dictates that they're stupid animals, because most people haven't spent any substantial amount of time with them and assume there isn't anything particularly interesting about their behavior, and because we have a vested interest in believing that there's nothing of value going on in their brains.

Thrustvectoring said:

I don't think that some animals are capable of suffering

From what Thrust has said, I think it's ambiguous between whether he cares he thinks animals can't suffer and doesn't care about them for that reason or he just doesn't care about animal suffering as you describe. Or , more likely, he is in some middle state.

As to your second point, yes that's the approach. And it seems largely that is what is happening when it comes up in the discussion here.