Lady Stefanie and her friend needed this slave to do some work for them. But he refused to do it and that irked the mistresses who had to put him in his place. He was trampled and gagged using their bare feet and when that was done, he was crushed on the face and made to remember his place. He apologized and told the mistresses he would never do it again.
Lady Stefanie felt that this guy deserved to be choked and she did so using her stinky socks. She did not care what the guy felt and she knew that it was important for her to punish him so that he never wanted to mess with her again. That is how he found himself licking her smelly socks and doing other cruel and humiliating things such as licking her boots.