Mistress Natasha was worried about her slave's new behavior. She had not punished him in a while and she was afraid he was beginning to take things for granted. So she punished him cruelly and she forced him to lick the soles of her boots. She made sure they were dirty before she made him lick them. That reminded him what a cruel mistress she can be if she meant to be and he refrained from doing things to piss her.