My very first Master had a discussion with me about the fine line between blackmail and humiliation. I think the conclusion we reached was that humiliation was a subset of blackmail, and could be done without the use of blackmail whatsoever. Most of the humiliating things he did to me, he had me admit that I wanted them, then change his mind and make me ask him, then beg him. Just that was humiliating enough, without what followed - which I asked for.