Goddess Andova likes to dominate people in all kinds of ways. That is why she had to make sure that she taught this naked slave a lesson that he would always carry with him. That is why the mistress used high heels to trample him. She did it while he was naked for the punishment to be more effective. He cried but she did not stop as she felt he had not learned enough.
Goddess Andova had tried times without number to get this guy to do things her way but he never changed. She got pissed and realized that she had to change tact so she used her high heels to punish him. And it was brutal as she sunk her heels into his skin at different parts of his body and forced him endure the pain and also learn that it was because of the things he did that she did not approve of.