This guy was nosy and this mistress felt that to make him stop, she had to dominate him. So she did it with her ballbusting skills and they worked like a charm. It was mostly because of the pain involved as the guy felt pain he had never felt before and he did not want to feel the same way again. So he changed the way the mistress wanted him to.
This slave had valuable information that the mistress wanted to lay her hands on but he refused to give it to her. The mistress tied him up but he thought she was bluffing. But she went ahead to kick him in the nuts and he wished he had never refused to tell her what she wanted because he was now in a lot of pain and he had to tell her.
When this mistress needed the services of this guy, he mistreated her because he felt he was in a position of authority. But soon enough, she did not need him and she sought help elsewhere. And she had to punish him so that he did not do the same to someone else. So she ballbusted him while he was tied up and he was naked. He never repeated that mistake.