In reality, the cages were enormous, over-engineered structures, ridiculously outsized for the animals they’d be holding. They weren’t mouse cages so much as mouse cities—huge tabletop-sized enclosures that could have housed German Shepherds. He spent most of his paper route money on the project, buying odds and ends that he needed: sheets of plexi, plastic water bottles, and small dowels of wood he used for door latches. While the other children in the neighborhood played basketball or wittedandu, Paul worked.

He bought exercise wheels and built walkways; he hung loops of yarn the mice could climb to various platforms. The mice themselves he bought from a pet store near his paper route. Most were white feeder mice used for snakes, but a couple were of the more colorful, fancy variety. And there were even a few English mice—sleek, long-bodied show mice with big tulip ears and glossy coats. He wanted a diverse population, so he was careful to buy different kinds.

While he worked on their permanent homes, he kept the mice in little aquariums stacked on a table in the middle of the room. On the day he finished the last of the big cages, he released the mice into their new habitats one by one—the first explorers on a new continent. To mark the occasion, he brought his friend John over, whose eyes grew wide when he saw what Paul had made.

“You built all this?” John asked.

“Yeah.”

“It must have taken you a long time.”

“Months.”

“My parents don’t let me have pets.”

“Neither do mine,” Paul answered. “But anyway, these aren’t pets.”

“Then what are they?”

“An experiment.”

“What kind of experiment?”

“I haven’t figured that out yet.”

* * *

Mr. Finley stood at the projector, marking a red ellipse on the clear plastic sheet. Projected on the wall, it looked like a crooked half-smile between the X and Y axis.