Lady Krasaviza was tired but she needed to punish her slave. She likes to punish a slave immediately a mistake has been committed so that he knows what he is being punished for. She could not let him go scotfree so she used her saliva to punish him. She knew it would not take a lot of time and effort to do it so she forced him to swallow her saliva as punishment.
This mistress wanted her slave to wank. She wanted him to do it for her own amusement not his. And she did not want him to use anything else other than her saliva. So she spat and gave him to lick and swallow her spit before he used her spit as lube to jerk off. To make it more interesting, she told him to jerk off to her instructions and the poor guy did.