Mistress Cai was angered to find out that her slave was smelling her underwear. He had a fetish for female underwear and he used that to masturbate. She hated that he did it using her underwear and she did not want a pervert in her house. So she humiliated him using her pee fetish. She made him drink her urine and told him that was what the underwear was covering and he should not have a problem with it.