But the lead hunter was no novice. As he settled onto the bull’s back, his hands were already pulling the spear upward out of its binding. As the bull began to react to the wounds inflicted by the other hunters, the rider jabbed downward with enormous power, and the spear seemed to go twenty centimeters into the animal’s spine.

It shuddered once and then flopped sideways, having lost all control of its muscles when its spinal cord was severed.

As it fell, the lead hunter sprang from its back, so he was not pinned under it.

Noxon thought back through what the man had done. In a single fluid motion, he had caught the bull’s horns, vaulted into the air, spun halfway around, landed on his feet, slid down into a tight-gripping straddle, withdrawing his spear and stabbing in the exact place with all his strength and leverage, and then leapt clear of the animal. In realtime it hadn’t been as rapid as it seemed in slicetime, but Noxon hadn’t been slicing that fast. It really had been unbelievably quick.

The other three hunters fell on the fallen animal instantly, using small stone blades to slice open the throat and belly. They disemboweled the animal and skinned it in smooth, practiced movements, each man knowing and doing his job. Noxon sped up his time-slicing enough that they could see the whole process before they needed to leave. When the men had the main cuts of beef and the aurochs hide wrapped in skins, and their spears and knives were fastened again to their bodies, Wheaton pumped his fist and Noxon and the others rose up and walked down the back slope of the hill they had watched from.

Noxon stopped slicing time, so they could talk again. “Need to see any more?”

In answer, Wheaton played back his own recording of the event. “I hope I can slow it down or at least take it frame by frame because there’s so much to see,” he said. “But I got it. A thing of beauty.”

They had been speaking in low tones. But the Neanderthals hadn’t survived this long by being careless or unobservant. Noxon looked over and saw that the beef-bearing hunters had spotted them. And, enhanced as his hearing was by the facemask, he could hear them talking. It wasn’t a highly advanced ­language—it consisted of names and single words. “Who.” “What.” “Enemy.” “Kill.”

How the Wall had given him the ability to understand such fragmented speech—from Neanderthals rather than Sapiens—would be a matter for Noxon to speculate about later.

“Disappear but stay in this time?” asked Noxon. “Or return to the future?”

“I have everything I need here,” said Wheaton.

The Neanderthals had already dropped their burdens of beef and, with spears in hand, were running toward the observation party.