Goddess Narcissra wanted this slave to eat her shit for breakfast. So she ordered him to do it and he was lost for words. He did not know what to do and he had to obey her as he knew that she meant business and if he did not obey her, he would be in for a worse ride. That is why she shit on him and made him eat her ass as well.
This mistress knew that there were many ways of torturing a guy without necessarily making him eat poo. So she did it to this guy but her method of choice was to force him to watch as she took a shit. The mistress knew that the sight of it was disgusting and so was the smell that came from it all. That is how the guy was humiliated and degraded.