Mistress Avery knew this guy was disgusted at the sight of someone else's spit. She wanted to use her spit to humiliate him as she was pissed at what he had done. So she called him to her house and she made him lick her smelly and sweaty socks before she made him open his mouth and she spat into it. She made him swallow all of it and enjoyed how he was degraded.
Degrading whoever she is not happy with is what this mistress does best. When this guy pissed her off, she used her feet to crush him. She had him lick the soles of her dirty high heels before she spat on him. That was to show disgust and she spat on his face repeatedly. After she was done spitting on him, she made him lick her spit and swallow it.
Madame Marissa and madame Madison spat on their shoes because they wanted them to shine. But they knew they were not the ones to make them shine. They made their slave lick the spit on the shoes till the shoes shone. It was only after he had licked spit off the shoes that they allowed him to use a shoe brush to shine the shoes like a pro. The shoes shone like they wanted.