Lady Scarlet had an issue with this guy and she punished him for it. But she was not satisfied with the kind of punishment she had given him and she had to find something else to give to him so that he would never be tempted to mess with her again. That is how she cruelly turned him into a human toilet and made him eat her shit. The punishment worked.
Lady Scarlet felt that eating shit was one of the necessary skills that her slave needed to learn. And she made sure he learned those skills. The mistress loved to punish losers by making them eat her poo and that is why she wanted this slave to learn those skills. So she waited until he had messed up before she made him eat her poo and he had to do it.