What is the difference between humans, animals and slaves?

My tribute to my friend Chris, author of the blog https://slavesthroughtheages.bdsmlr.com/

What is the difference between humans, animals, and slaves? 

It is not intelligence; there are intelligent animals and stupid humans, nor form; there are beautiful and hideous beings in both universes. Therefore, it is not a question of nature or philosophy but law. Roman laws established that citizens were only free men; below them came women and children, considered incapable; below these animals (horses, oxen, and dogs); below animals, slaves, compared to objects, and as such, they were classified as functional and useless.

The law established that slaves, as objects, had no rights and could be used, destroyed, or disposed of like anything else that belonged to someone.

These creatures were used, tortured, and discarded without any restrictions or concerns. The drawing shows two people, a Roman citizen crossing the street with his litter and a woman walking calmly. The citizen must be thinking about his social commitments and the woman in her tasks.

The beasts that carry the litter ensure that their owner's walk is comfortable and without many shakes. The leather of the beasts, tanned in the sun, exposes the marks and scars of countless whipping beats for each failure in the fulfillment of its functions. Upon arriving at his home, the citizen will inform the butler if the beasts should be whipped again and how many lashes each one will receive for the trip stumbling.

Like animals, these beasts defecate and urinate while carrying their burden. Like despised beasts, they cry in pain and fear and bleed for the failures they make.

The paving of the streets was irregular; it was not uncommon for the beast to be flogged to death for dropping the literature on the way.