Word Choice – Is There a Word for an Intelligent, Self-Aware, Sentient Lifeform?

Eloquent comes to mind for a well-spoken orator or a good communicator.

The opposite is a little trickier. Searching on thesaurus.com for the antonym of eloquent I found inarticulate and unintelligible though I'd be careful using such terms about your boss. A more tactful way of describing a semi-literate person such as your boss would be to say that he doesn't exactly have a way with words.

Cruel is possibly the most often used adjective for this context, though from my experience cruelty (as a noun) is more common. (E.g. SPCA stands for the Society for the Prevention of Cruelty to Animals.) The Wikipedia article is called Cruelty to animals and says that it is also called animal abuse or animal neglect.

Though there is no such word used exclusively for animals, we are not much the worse for the lack, since context will dictate the meaning of any word we choose when describing cruelty to animals. For instance, if someone spoke of "inhumane treatment of animals", we would not think he meant "not suited for human beings"; we would understand that he was referring to cruelty to animals. This shows that many synonyms of cruel/inhumane can be used and understood properly.

It's worth noting that even if the word inhumane is not commonly used to describe cruelty to animals, humane appears to be most often used as its antonym, as in the Humane League, Humane Society, or humane treatment.