For me the biggest turn-on is not knowing what's going to happen. One of my fave visits was with an RMT who's now retired. She'd always have some excitement on hand; it could be orgasm denial and control, forced multiple orgasms, forced servitude, being restrained and about a million other things. I've had this type of relationship with more than one RMT, but the one who really drove me crazy was the one who was most verbally reserved. She didn't say much of anything; what happened, happened because of her will, not her words. Giving up control like this is extremely erotic.