This mistress had a slave who did not like to work hard. He had been a hard worker before but he had changed and become a lazy one. So in an effort to make him work as hard as he used to, she used her shit and her pee to do it. It was cruel and degrading but she did not care and he had no choice but to eat it.
This guy was insensitive and this mistress had to do what she considered to be the best punishment in the circumstances. She turned him into a human toilet and he had to eat her poo as well as drink her pee. There was no way out and he did not have much choice but to do the things she had asked him to do. He was even gagged with a dildo.
When this mistress asked this guy to eat her shit, he refused and she was pissed. She did not want him to be comfortable saying no to her and think that it was ok. So she did what she felt was what she needed to do in order to make him fear her and do what she wanted. The mistress crushed his face with her feet and that is how she got him to eat her shit.