The slave has to implore for mercy

This asshole slave deserves to be smothered, so firstly I plug his nose with a clothespin so that he can breathe only through his mouth. Then, I begin submitting him to a prolonged suffocation by introducing forcedly my feet into his mouth in order to impede him to breathe. The torture will end only when the slave will have the strength and breath to implore for mercy at his Mistress.