When Sherlock stops moving, John trails his hand down the side of Sherlock's hip. He goes over the bone, and then down his thigh, sliding towards his inner thigh, and then stops, waiting and watching for a reaction.
For a moment, John is silent. He wants to hear Sherlock beg. He doesn't know why, but the little sounds Sherlock makes, and the sound of his voice asking John to continue just sparks something inside of him.
Finally, he speaks. "Tell me what you want me to do, Sherlock." John's voice is a whisper, and all signs of nervousness have pretty much disappeared.