"Let's go swimming," Lilly said.
"We haven't unpacked our swimsuits," Amy replied.
"So?" Lilly walked to the shore of the pond, stripped naked, and went running in.
Christie and Amy looked at each other, grinned, and did just as Lilly had.
If there had been any boys around, Christie would never have dared go skinny-dipping. But, since it was just the girls, she joined in with abandon.
After a while, Christie, kicking and moving her arms in the water, looked at her friends. "I am so glad we came," she said.
"Us too," Amy replied. "How come you're swimming so hard?"
"To stay afloat, of course." Then, she noticed that the other girls weren't doing that. "How are you staying up?"
Lilly looked at Amy. "We're just standing on the bottom."
"What?" Christie dove down for a better look. Sure enough, Amy and Lilly were just standing on the bottom, which was too far underwater for Christie to do the same. But we're all the same size, she thought. Aren't we?
Are we?
Christie swam to the shore, and ran to where she had left her clothes. Holding up each article of clothing, she found it was now too big for her.
"Christie?"
Christie turned. Just a few days ago, she had been the same size as Amy; now, Amy's nipples were at Christie's eye level.
"Christie," Lilly said, "you're... "
"Shrinking," Christie said, finishing the thought.