The way to distinguish an animal from a non-animal

I sometimes agree with Thomas Reid's philosophy, and I sometimes don't. He's big into the importance of common sense, which can be refreshing. But I've just read a very, very perplexing claim. It seems to me to have no basis at all in common sense. This is from Essays on the Active Powers of Mind, V: Of Morals, Chapter 7.

Feeling, or sensation, seems to be the lowest degree of animation we can conceive. We give the name of animal to every being that feels pain or pleasure; and this seems to be the boundary between the inanimate and animal creation.

This point is not critical to Reid's argument, but I'm baffled as to why he would think this is true. Anyone see any plausibility in it at all?