Mistress Anni did not want to introduce any inconsistency in her life and that is why she opted to use her sneakers to do it. It was fun for her and she had a great time torturing this loser. She made him do things her way and gave her instructions on how he was to lick her sneakers. He obeyed it all as he did not want to piss her off.
Mistress Ann needed to tame this loser and she did it with her sneakers. The mistress was wearing her sneakers so all that she did was to have him kneel down and lick the dirty soles of her sneakers. It was not optional for him and he had to do what the mistress asked him. The humiliation made him learn to respect and obey her at all times to avoid being punished.