The hammer rang once. A spark jumped off the anvil and did not go out. It waited. They followed.

Beto was helping clean the mending shed. He shook the old string mop. Its floppy strands flew everywhere. The handle had split long ago and been bound tight with twine, and above the twine somebody had scratched a tiny hammer.

"These are the bit that works," he said. "If they were stiff, they wouldn't pick anything up."

Danya watched the strands swing. "So floppy can be useful," he said. "How do we know?"

The spark slipped through the museum's back door into the workroom where the Sketcher and the Photographer work. They followed.

Margit was at her table with a new page of letters.

"Ink where I'm sure, pencil where I'm not," she said.

She inked the middle of the chain in firm black lines: two spirals and a fold. Then she reached the end of the letters, and her pencil went very light. She drew a long, wandering tail, so faint it was hard to see.

"How much of it is pencil?" asked Danya.

Margit counted. "Thirty links out of a hundred and twenty."

"A quarter," said Danya.

Beto took the rubber from the table. "That tail is a mess," he said. "It's a mistake. I'll tidy it."

"Pencil means I don't know yet," said Margit. She put her hand over the page. "It doesn't mean I'm wrong. If you rub it out, you rub out what I don't know. Then we can't check it."

Beto put the rubber down. "So the faint part is still a clue?"

"Show me the photograph," said Margit. "I want to be wrong if I'm wrong."

Kemi came out of the cold room with frost on her gloves.

"I took it in the cold," she said, and laid her picture on the table.

The middle was sharp. Two spirals and a fold, just as Margit had inked them.

But the tail was a smudge. A long grey blur, with no clear edge anywhere.

"Is your camera broken?" asked Beto.

"A blur tells you something too," said Kemi. "Where it moved, my picture blurs. This tail would not hold still, even frozen."

She explained how she worked. She froze a drop of water with many copies of the protein inside. Then her microscope took thousands of pictures, and she added them together. Where every copy looked the same, the picture came out sharp. Where every copy was a little different, the picture came out soft.

Danya put the two pictures side by side.

"The pencil tail and the blurry tail are in the same place," he said. "How do we know what that means?"

"My letters didn't tell me one shape," said Margit. "So I drew it faint."

"And it never took one shape," said Kemi. "So it photographed blurred."

They had found the same thing two different ways. The tail was floppy. It moved all the time.

Beto thought of the mop. "Like the strands," he said. "A moving tail can reach out. It can bump into a partner and hold on."

"Some floppy tails do exactly that," said Kemi. "They're the part that catches."

Margit looked happy. She had been unsure, and that had been the honest thing to be.

They pinned the second pair to the board. A pencil tail on the left. A blurred tail on the right.

The spark slipped back out through the museum door, and the workroom was dark again.

Back on the Green

The spark dimmed to a warm dot and settled back on the anvil. The Green was just the Green again.

At football, Danya's coach asked who would play where. Danya said he wasn't sure yet. He wrote it in pencil on the team sheet, and changed it after the first half.