The teacher nodded. "Good. Make certain the edge is sharp. Next?"
"A candle." There was snickering in the back of the classroom. "A lit candle."
"Very good. Next?"
"A… a glass of water."
"Good. The shape of the glass, the transparency. The boundary between glass and water. Take care. And you, Penelope?"
The little girl's eyes turned back from the window. "A butterfly."
One of the others objected, "You can't do a butterfly, that's too hard."
Penelope snapped petulantly, "I can so!"
The teacher raised her hand, and there was quiet. "Go ahead, Penelope. A living butterfly."