Mistress Iside likes to know people's pain thresholds as she works with them because it shows her and it tells her how to deal with them in the event that they piss her off or she needs to torture them. So the mistress tied this one up and she used her boots to ballbust this guy and make him feel pain that he had only heard about up until that point.
Mistress Iside values loyalty and that is why she was pissed when her slave backstabbed her. She could not reconcile all that she had done for him with what he had done for her. The mistress had to find a way to deal with him and she did so using her ballbusting fetish. He was stripped naked and kicked so hard in the butt that he nearly shit his pants.