Lady Rockabella wanted to humiliate this guy and she did it with her saliva. She made sure that he learned his lesson the hard way. With the mistress being someone who is a bit quiet and reserved, the guy thought that she was harmless. But he regretted that immediately as the mistress shocked him and did humiliating things to him without batting an eyelid in the process of it all.
Lady Rockabella was not pleased that her slave was lazy. She had to make sure he learned to do things her way and work as hard as she wanted him to work. So she degraded him by forcing him to lick her saliva and also swallow it. She told him that if he did not change, she would have no issue upgrading his punishment and doing more and worse things to torture him.