Goddess Andova was conned by this guy and she had to get her revenge. She knew that since she was not a con, she would not get her revenge in the same way. So she laid a trap for him and when she caught him, she used her spit fetish to dominate him. The mistress turned him into a spit slave and had fun torturing him like she had never done before.
When she looks for a slave, she knows what he wants. She knows what will drive him insane with the desire to bow to her wishes. She knows that he wants her warm, slimy spit. She is happy to sit in front of a potential slave and spit into a jar. If he doesn't want to play in her spit, she knows that he is not the slave she needs. When she finds him, he will give her anything to get that warm jar of spit.