"I think that a psychological scale of arousal," she continued, "would have to take into account how close a man is to cumming."
Tom looked at her, puzzled.
"Look at you," she argued, "You're hard, but not ready to cum yet. But if you masturbated, then you would be more ready to cum, even if I put your cock in ice!"
Tom was captivated with these thoughts, but he was also trying to get his mind off of Penny and her tease, so he tried to concentrate on her argument. Eventually he said he was pretty sure that hardness and arousal were strongly correlated.