Those were the four words he whispered gently in slaves ear while watching her reactions. He went on to explain the change in ones eyes when things get particularly unbearable. The look of surprise when the intensity pushes a little bit past where one thought it could actually go. He continued to explain how much it pleases him, how much he loves the way slave kisses when she is in so much pain.
Before his words there was a bit of panic (yes we have a safe word, but it was not needed) as ones legs were kicking about in a desperate kind of way of processing the pain. Legs that were slippery from the excitement of it all. After those words there was just calmness as she absorbed it all knowing how much it pleased him. And of course there was a lot more wetness.