Avodah Zarah 16: A Lion Is Not a Work-Horse

Selling horses to idolaters: Because the horse can be used for labor that isn't subject to violation of Jewish law. Also, a new mishnah prohibiting the sale of wild animals that might cause public injury -- with exceptions when the animal wasn't a risk, for whatever reason. Plus, a prohibition against building structures that would house idolatry, though other building may be acceptable.