Lady Nora wanted to try something she had not done before. She wanted to try femdom spitting because she did not have any experience doing it but it seemed like it was fun. So she used her femdom spitting fetish to do it. The mistress had to get a loser to do it with. She humiliated him and that she had fun at his expense despite him not doing anything to deserve it.
Lady Nora was out to teach this guy how to lick spit and she felt that the best thing he could do was to follow her instructions. She had to make sure he became good at it and that he did it soon. That is why she did what she did to him and why she had fun at his expense. He was scared shitless and he did what she wanted.