Not what you think

"Well?" Karyn asked Jon, who was checking himself for any changes.
"Let's see... nope, no tail" he said while feeling his backside.
"No pointy ears or fangs", feeling his ears and teeth.
"Give me a hint" Jon asked.
Karyn, about to burst from laughter said, "follow me into the bathroom" as she stood up and jogged over there.
Jon jumped down from the couch and hurriedly followed her, his much shorter legs not able to keep up.
"Slow down, you know I can't keep up with you." Jon called after her as he ran to catch her.
When he got there, she was sitting on the edge of the tub waiting for him. She reached out her arms and said, "Come here, I'll show you the change". He climbed up into her lap and she stood up holding him to her side and faced the mirror.
"See?" Karyn said.
"See what?" Jon asked, getting annoyed. "All I see is what I always see, two girls who look exactly alike, except you're twice my size. What did you change?"
Unable to contain herself, she handed her mini twin the paper. Jon took it into his tiny hands and read it: "Jon is my half size twin". Suddenly the real memories came flooding back to him.
"Very funny", he said suddenly very self concious about his size compared to Karyn. "Change me back"
"Sure", Karyn said, "Just take the pencil", as she held it over her head way out of Jon's reach. He jumped up to get it and slipped on the sink, landing on his ass. His new breasts, which felt so natural only moments ago felt very uncomfortable as they shook with the impact. Karyn reached up and put the pencil on a high shelf then turned her attention back to her mini twin.
"Now, how about we have some real fun?" she asked as she placed each hand around his chest and massaged his ping pong size breasts with her thumbs.