These mistresses had stinky socks and sweaty feet. Those are the things that the mistress wanted licked by this slave and he had no choice but to do it. He knew better than to argue with them so he did not even try to do so as he knew what would happen if he did so. The mistresses had a great time torturing him and it was a lot of fun.
This mistress wanted her boyfriend to learn to do things her way because whenever he insisted on doing things his way, he ended up messing things up. She was fed up with correcting him all the time and he had to sit back and let her take the lead. She enforced that rule by turning him into her foot slave. He had no choice but to lick her feet and her socks.