Mistress Anni needed to pass her message across and she did this with her sneakers. She had tried talking to this guy but she felt that he did not listen to her and she did not want to continue wasting time talking to him. That is why she chose to make him lick her sneakers and trampled him a little with the same sneakers. He got the message she was passing across.
Mistress Anni wanted this slave to know that it was wrong to betray someone else's trust and that is why she opted to dominate him. He had to feel pain and he had to be humiliated by the mistress in order for the message to go out. The guy did not expect what the mistress did to him and he learned his lesson. He never betrayed anyone else's trust after that.