Sacred Haven of Debauchery

So, what is the difference, and does it even exist?

A slave is more intelligent. Strictly speaking, a slave is primarily a servant who works not under a contract, not for a fee, but out of obligation and has no choice whether to work or not. The treatment of a slave, as an object or as an animal, with all the consequences, if I understand correctly, did not always and everywhere take place. This is a secondary quality.
Accordingly, a slave performs the functions of a servant. He can be entrusted not only with performing some work, but, if there is trust, also with rather intellectual functions, for example, managing the owner's finances, and so on. An animal can only be entrusted with work, and only the most elementary, and in most cases, even this cannot be entrusted; instead, the animal is used as raw material, an element of decoration, or something similar. Well, you can also develop a warm relationship with it, though.