Best movie reference I have for a BDSM related movie that isn't a documentary is the movie The Secretary, it has Maggie Gyllenhaal in it, and is a bit strange and quirky but I think it is really sweet.

As someone who is a submissive and very much in a happy healthy relationship with my Dominant aka my boyfriend, I enjoy spanking. I don't see it has hateful or violent, it is an expression of his control over me, of me showing my trust that he won't actually hurt me. For some people it is about the pain, the scientific explination for that is when we endure pain it releases endorphins the feel good chemical in the brain, so with pain comes of rush of euphoric emotion.

It all varies from individual to individual, I am not really big.into pain, spanking, slapping, anything in those lines I enjoy because of the act of dominance that goes with it, the sense of release of control.to another person that I love and trust and I know will keep me safe. For some people it is about the pain, for some it is both, and for others it is something completely different. The best thing you can do is ask your friend why she likes it, what does.it do for her on an emotional level?

I know when a lot.of people talk about D/s the thought of control seems really odd, but if you were to talk to me or my boyfriend you would.find our relationship is pretty non kink, not every waking momwnt of my day is spent waiting for him to give me an order. I work, I go to college, I spend.time with friends, I visit family I do make decisions for myself. We also hold hands, have silly pet names for each other, celebrate our anniversary, surprise each other with little gifts, etc. The only differnece besides the sexual stuff is we have agreeded together that he gets final say in decisions, he listens to my opinion and makes a decision from there, he is in charge of the finances, he keeps me on track with school and guides me along.

Dominance and submission is different for every person in the BDSM community, just like every "vanilla" (non BDSM) relationship is different.