Does the slave really believe that he can just lick his Mistress' shoes clean with only his tongue? Mistress Roxana want to make sure the job is done properly so and spits on the soles of her shoes to loosen the dirt before holding them in front of the slave's face again. Now lick them completely clean! There must not be a bit of dirt or spit left on her soles!
Mistress Anfisa has let her slave starve, just so she can feed him now. She sadistically enjoys seeing him lying on the floor in front of her, looking at her grapes with begging eyes. He wants to eat them so much and Mistress Anfisa even gives him some of them! But surely differently than he expects... namely pre-chewed with plenty of her spit! She spits the chewed grapes on the floor and then lets the slave lick up this exquisite grape juice. Hmmm... yummy!
The despair is clearly written in the slave's eyes. He's been sitting tied to a chair for such a long time and is so thirsty that he would drink anything! Mistress Anfisa knows this well and spits in his mouth and pitiful face. She grants him a few drops of spit to quench his thirst. Any other drink is simply not allowed!