Cathy could feel Paul's penis getting soft. And, while of course this was completely normal, she still wished it'd stay hard. Strangely, the moment she thought that, she noticed it had stopped getting soft, and was actually getting hard again.
"Woah…" she said. "What?" Paul asked, not yet realizing anything was amiss.
"Your dick. It's not getting soft"
"Huh, that's cool I guess?"
Cathy started to move up and down on it. "Does it feel good?" she asked. "Not particularly." he replied.
Cathy had an idea. "I wish he had a refractory period of 1 minute", she thought.
"Oooh, now it does kinda feel good", Paul said.
"Oh dang… that's cool!" Cathy said.
"What? What happened? What's going on?" Paul asked. He was very confused, though not exactly unhappy with this strange turn of events.
Cathy started riding him again, and within a minute she could tell he was at the brink of orgasm. She held him there as best she could, but one minute wasn't nearly long enough for her to get back to orgasm, at least not given the short break and all the excitement of exploring the transformations. Unfortunately for her, Paul went off again before she could build back up to another orgasm. "Hmmm… maybe I just need to be more sensitive," she thought. "I wish my vagina was twice as sensitive", she thought.
Her previous transformation of Paul seemed to have held, so he never got soft after going off the second time, so Cathy kept going, but she didn't feel any different. Paul was very confused how he could have experienced a second orgasm so quickly, so he finally snapped out of the spell of arousal, pulled out of Cathy, and asked, "what's going on? I just came twice in like, two minutes. How is that possible?"
Cathy explained what she had figured out so far. "It was the lubricant I used. I got it in a magic shop. I thought it just made you hard, but it seems like after you came in me, something else started happening. I've been able to kinda control aspects of your body. But not mine."
"Psh, what?" Paul said. "C'mon, that's ridiculous!"
"Yeah… I know, but humor me for one second. Just think about one thing you'd like to change about me. It might help if you explicitly think 'I wish' as part of the thought"
"OK… sure"
Paul was a big fan of Cathy's curves, but he'd always wished her legs were longer, so he started with that. "I wish her legs were long and thin", he thought.
And sure enough, Cathy's legs began to grow. Without losing her curves, her legs gained about 3 inches and slimmed up a bit. It was a bit hard to tell if anything had happened with them both on the bed, so Paul requested that she stand up. She got off the bed, and Paul jumped off too, standing beside her. He could tell the difference. There was no doubt; Cathy was definitely taller, and her legs more slim too.
"Holy shit!" Paul said. "You were right!"
With that, Cathy leapt up on Paul and started making out with him, and they both went to town changing each other's bodies…