Mistress Dula and her friend wanted to put this guy in his place. That is why they specifically chose to use muddy shoes because they knew he did not expect it. He was made to strip naked and the mistresses then had him lick their muddy soles. He was threatened with trampling if he did not lick the soles clean so he did it to avoid the pain of being trampled.
Mistress Aurora does not like sitting behind a desk all day to make money. She decided she had to make a living out of what she loved and what she loved is being a sadist. She loved making others miserable so she curved out a niche for herself whereby she was paid to punish and humiliate people. And today she was paid to make this girl lick mud from her boots.
Mistress Zora found out that her slave was not easy to tell something as he did not listen. She had to teach him to listen and to take instructions. So the mistress did this by forcing him to lick her muddy shoes. He was humiliated and dominated but he learned his lesson the hard way and he did what she asked him to. He never messed again as he knew what would happen.
Mistresses Courtney and mistress Suzanna are the kind of people you do not need to mess with if you know what is good for you. These mistresses love to torture and they use any slight reason to torture someone and teach them a lesson they will never forget. And that is what happened to this loser as he was forced to endure being stomped and crushed using muddy shoes.