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But in a regular nerve cell, the dendrites don’t latch onto other nerve cells, muscle cells and membranes, and they certainly don’t reach out and pull.

Regular nerve cells, you see, don’t crawl.

The crawlers implemented a very simple navigation system: cause pain. This was a practical strategy, not a s.a.d.i.s.tic one: the human body is wired to give pain messages the highest priority. The crawlers’ stretching dendrites reached out, locked onto axons, then released a chemical that mimicked normal pain signals. Some nerves ignored this message—those were the efferent neurons, the ones that carried signals from the brain to the rest of the body. Also called motor neurons, they let the brain do its thing, controlling muscle reactions and bodily functions. The nerves that did not ignore these messages of pain, but instead replicated them and pa.s.sed them on to the brain, those were the afferent nerves.

Once the crawlers identified afferent chains, they grabbed, and pulled, and crawled. Every three or four nerves, they released the pain signal again, measured the results and kept moving.

Eventually their crawling would lead them to the brain.

UNKIE DONNY DEPARTS

Fluffy snow blew lightly in all directions, flying into Chelsea’s eyes and tickling her nose.

She didn’t feel good. She felt kind of hot, achy, and she had some little b.u.mps on her hands. Those hurt a bit, but didn’t itch or anything. She held her daddy’s hand as Unkie Donny and Betty got into Unkie Donny’s car. Betty blew her nose into a pink Kleenex, then put her head back on the car seat and closed her eyes. She didn’t feel good, either.

Unkie Donny shut the driver’s door and rolled down the window. He coughed hard, a rattling sound in his chest, then stuck his hand out of the window toward Daddy. Unkie Donny’s breath billowed out as he talked.

“Little brother, thanks for having us,” he said to Daddy. “And thanks for the gift that keeps on giving.”

“Oh, put a sock in it,” Daddy said. “You imported the creeping crud from Pittsburgh. I’m not shaking a hand you just coughed in.”

Unkie Donny’s eyes narrowed. “What the h.e.l.l is that supposed to mean?”

Chelsea took a step back. Unkie Donny suddenly looked kind of scary.

“I’m just teasing,” Daddy said. “Relax, big brother.”

Unkie Donny stared for a few seconds, and then his face softened. He blinked a bunch, like he was waking up or something.

“Sorry, man,” he said. “I . . . I guess I really took that the wrong way.”

“Meds?” Daddy said.

Unkie Donny nodded. “Took them. Honest.”

“Cool,” Daddy said. “We’ll come down to Pittsburgh sometime soon.”

Unkie Donny’s eyes narrowed again, then opened again. He shook his head the way a puppy would.

Mommy stepped forward and leaned in the window to give Unkie Donny an awkward hug. “Drive safe,” she said. “This storm is supposed to turn into freezing rain. The roads are full of downstaters, and the traffic is going to be terrible. Watch out for the drunks.”

She backed out of the window. Unkie Donny smiled and nodded.

Mommy went around the other side of the car to say good-bye to Betty. Unkie Donny looked right at Chelsea. He held out his hand.

“Come here, dolly,” he said. “Say good-bye to me.”