Black Ice

"And be careful not to skate on the black ice," warned Mother as she gave the twins their skating bags. "You'll fall through."
"We won't, Mama, I promise," said Jennifer.
"Me too," said Lucy.
So the twins walked and walked and walked in the cold winter weather until they came to a frozen pond."Let's begin," said Jennifer.
"Me too," said Lucy.
It was quite a large pond, so Jennifer went skating around it to make sure was safe.
"Fine, except for some black ice," she reported when she came back.
"Well, we can just skate around it," said Lucy.
They skated for a few minutes until Lucy said,"Jennifer, go skate on that black ice."
"No," said Jennifer, "you do it."
"Me too," said Lucy.
So Lucy went over the black ice and easily skated over it. "Now it's your turn," she told Jennifer when she came back.
Jennifer went to the black ice. When she was halfway through skating over it, there was a sudden crack.
"Uh-oh," said Lucy.
She quickly skated over to the black ice just in time to grab Jennifer by the arms and pull her out. Then they warmed each other up until the only evidence of them having an encounter with black ice was their hands: they had turned black.
When they got home, Mother asked them, "What have you two been up to?"
"Nothing," they both innocently said, hiding their bare hands behind their backs.