"Jon, how could you?" asked Karyn. "I thought that for the next week you don't mind having your body anyway? Why would you do such a thing to me?"
"Oh, come on, Karyn, it's just a guy's lower half, it's not like I turned you into a Klingon or something."
Then Karyn realized the mistake in her suggestion. For the next week, Jon won't mind having his body, mostly. That must be because he didn't think of partial sex changes as a big thing. It seemed he didn't think of anyone's changes as a big thing! So Jon changed Karyn's body as casually as he would, oh, make a funny face at her.
"Wait," said Karyn, "I have an idea. You still want to change back to a guy again, right? You'd still take the chance?"
"Sure."
"So why don't we trade lower halves? I know that they're not exactly the same as our original bodies but later on you can wish to fix that."
"Hmm," said Jon. "Okay. I wish that my lower half and Karyn's would swap."
Suddenly there was no bulge in Karyn's pants. And Jon was all guy, as far as she could see. It still seemed strange for Jon to be all guy, since Karyn didn't remember him that way, but she could ask for a wish to help with that.
"Well, that does it," said Jon, "so... Argh."
"What is it?"
"I'm still changing!" replied Jon. He knew without even looking down, but he looked down anyway. Female curves, and he felt nothing between his legs--at least nothing pressing against his pants like male parts might. "I'm a girl down there again!"
"How can that be?" wondered Karyn.
"I don't know... Oh. Now I get it," said Jon. "I wished your lower half would be male until I became a complete guy again. Getting your lower half made me a complete guy. And that made your lower half change back to female again."
"Well, we're no worse off than before," said Karyn. "I'm a girl, you're like I remember you."
"No, we are worse," said Jon. He raised his leg and pulled back an inch of his pants leg. "First, our lower halves don't even match our upper halves. Look, there's not a lot of hair here, but what there is is blonde. And next, my periods. Suppose I made a mistake and I'm not having periods because I'm pregnant. Well, now you are instead...."
