Madame Marissa had to teach her slave not to think that he could do whatever he wanted. That was wrong and he had to know that there were rules and regulations he had to follow. That is why she used her riding boots to trample him. He had to lick the soles of her muddy riding boots before the mistress felt that that was enough time for him to learn his lesson.
When this slave became disobedient, he did not count on the mistress punishing him. The mistress had to punish the guy and she did it with her riding boots. The guy could not believe what was happening to him as things did not go according to script. He was used to disobeying and she did not do anything about it. That is why she was shocked by what the mistress did.