Mistress Clarissa needed to show this slave that she was not the kind of person to be messed with and to turn the other cheek. She had to make him learn that he would be punished cruelly if he pissed her off. That is why she cleaned her dirty feet on his mouth and she made sure that he licked all of her feet until they were as clean as she wanted.
Mistress Sharon was angry at her boyfriend and she made sure that he would not piss her off again the way he had. She was so angry at him that she felt that the best way to deal with him was to force him to lick her feet which were dirty. He did not think she could ever make him do that but she did and he had no choice but to comply.
Mistress Darcia had to make sure that her ex learned that she had moved on and wanted nothing to do with him. That is why the mistress made sure that he learned his lesson and would not piss her off again. He was trampled, kicked and made to lick her feet. Her feet were muddy to make it even more humiliating for the guy. He had no choice but to do it.
Mistress Electra needed to torture this guy and she did it with her worms. The mistress had to make sure that he learned that she was not to be messed with and was rather to be obeyed at all times. That is why the mistress chose to trample him and to make him lick mud and worms from her feet. The guy had no choice but to do it all.