This mistress did not want to deal with a loud slave. She had to do everything in her power to make sure that the guy learned his lesson. He had to endure the degradation he felt from her and that is how she ended up teaching him the lesson of a lifetime. She scared the shit out of him and she laughed at him as she saw him scared shitless.
Goddess Nemesis wanted to communicate to this guy and she did it with her spit. She had tried to use her words but she felt that she was not getting anywhere with him. That is why she had to change tact and she did what she did. The guy was shocked but he could not do anything about it and he had to endure all the humiliation she put him through. He got the message.