"I hope for you that you'll get to cum at the 50th stroke, otherwise all of it would have been useless!"
"And don't forget to really crush your pathetic balls at the last stroke! Make them hurt as hell! I want the pain to make you even forget the pleasure of cumming!"
"Oh and if you don't succeed to cum at 50th stroke, then just leave. I'm not interested into slaves who don't listen their mistress"