"They have memory?"

"Yes, they have memory. Limited. We built it in." Ricky pressed the button on his radio. "Anybody hear anything?"

The answers came back, crackling in his handset.

"Not yet."

"Nothing."

"No sounds?"

"Not yet."

I said to Ricky, "It makes sounds?"

"We're not sure. Sometimes it seems like it. We've been trying to record it…" He flicked keys on the workstation, quickly shifting the monitor images, making them larger, one after another. He shook his head. "I don't like this. That thing can't be alone," he said. "I want to know where the others are."

"How do you know there are others?"

"Because there always are." He chewed his lip tensely as he looked at the monitor. "I wonder what it's up to now…"

We didn't have long to wait. In a few moments, the black swarm had come within a few yards of the building. Abruptly, it divided in two, and then divided again. Now there were three swarms, swirling side by side.

"Son of a bitch," Ricky said. "It was hiding the others inside itself." He pushed his button again. "Guys, we got all three. And they're close."

They were, in fact, too close to be seen by the ground-view camera. Ricky switched to the overhead views. I saw three black clouds, all moving laterally along the side of the building. The behavior seemed distinctly purposeful.

"What're they trying to do?" I said.

"Get inside," Ricky said.

"Why?"

"You'd have to ask them. But yesterday one of them-"

Suddenly, from a clump of cactus near the building, a cottontail rabbit sprinted away across the desert floor. Immediately, the three swarms turned and pursued it. Ricky switched the monitor view. We now watched at ground level. The three clouds converged on the terrified bunny, which was moving fast, a whitish blur on the screen. The clouds swirled after it with surprising speed. The behavior was clear: they were hunting. I felt a moment of irrational pride. PREDPREY was working perfectly! Those swarms might as well be lionesses chasing a gazelle, so purposeful was their behavior. The swarms turned sharply, then split up, cutting off the rabbit's escape to the left and right. The behavior of the three clouds clearly appeared coordinated. Now they were closing in. And suddenly one of the swarms sank down, engulfing the rabbit. The other two swarms fell on it moments later. The resulting particle cloud was so dense, it was hard to see the rabbit anymore. Apparently it had flipped onto its back, because I saw its hind legs kicking spasmodically in the air, above the cloud itself.

I said, "They're killing it…"

"Yeah," Ricky said, nodding. "That's right."

"I thought this was a camera swarm."

"Yeah, well."

"How are they killing it?"

"We don't know, Jack. But it's fast."

I frowned. "So you've seen this before?"

Ricky hesitated, bit his lip. Didn't answer me, just stared at the screen.

I said, "Ricky, you've seen this before?"

He gave a long sigh. "Yeah. Well, the first time was yesterday. They killed a rattlesnake yesterday."

I thought, they killed a rattlesnake yesterday. I said, "Jesus, Ricky." I thought of the men in the helicopter, talking about all the dead animals. I wondered if Ricky was telling me all he knew.

"Yeah."

The rabbit no longer kicked. A single protruding foot trembled with small convulsions, and then was still. The cloud swirled low to the ground around the animal, rising and falling slightly. This continued for almost a minute.

I said, "What're they doing now?"

Ricky shook his head. "I'm not sure. But they did this before, too."

"It almost looks like they're eating it."

"I know," Ricky said.

Of course that was absurd. PREDPREY was just a biological analogy. As I watched the pulsing cloud, it occurred to me that this behavior might actually represent a program hang. I couldn't remember exactly what rules we had written for individual units after the goal was attained. Real predators, of course, would eat their prey, but there was no analogous behavior for these micro-robots. So perhaps the cloud was just swirling in confusion. If so, it should start moving again soon.

Usually, when a distributed-intelligence program stalled, it was a temporary phenomenon. Sooner or later, random environmental influences would cause enough units to act that they induced all the others to act, too. Then the program would start up again. The units would resume goal seeking.

This behavior was roughly what you saw in a lecture hall, after the lecture was over. The audience milled around for a while, stretching, talking to people close to them, or greeting friends, collecting coats and belongings. Only a few people left at once, and the main crowd ignored them. But after a certain percentage of the audience had gone, the remaining people would stop milling and begin to leave quickly. It was a kind of focus change. If I was right, then I should see something similar in the behavior of the cloud. The swirls should lose their coordinated appearance; there should be ragged wisps of particles rising into the air. Only then would the main cloud move.

I glanced at the timeclock in the corner of the monitor. "How long has it been now?"

"About two minutes."

That wasn't particularly long for a stall, I thought. At one point when we were writing PREDPREY, we used the computer to simulate coordinated agent behavior. We always restarted after a hang, but finally we decided to wait and see if the program was really permanently stalled. We found that the program might hang for as long as twelve hours before suddenly kicking off, and coming back to life again. In fact, that behavior interested the neuroscientists because"They're starting," Ricky said.

And they were. The swarms were beginning to rise up from the dead rabbit. I saw at once that my theory was wrong. There was no raggedness, no rising wisps. The three clouds rose up together, smoothly. The behavior seemed entirely nonrandom and controlled. The clouds swirled separately for a moment, then merged into one. Sunlight flashed on shimmering silver. The rabbit lay motionless on its side.

And then the swarm moved swiftly away, whooshing off into the desert. It shrank toward the horizon. In moments, it was gone.

Ricky was watching me. "What do you think?"

"You've got a breakaway robotic nanoswarm. That some idiot made self-powered and self-sustaining."

"You think we can get it back?"

"No," I said. "From what I've seen, there's not a chance in hell."

Ricky sighed, and shook his head.

"But you can certainly get rid of it," I said. "You can kill it."

"We can?"

"Absolutely."

"Really?" His face brightened.

"Absolutely." And I meant it. I was convinced that Ricky was overstating the problem he faced. He hadn't thought it through. He hadn't done all he could do. I was confident that I could destroy the runaway swarm quickly. I expected that I'd be done with the whole business by dawn tomorrow-at the very latest. That was how little I understood my adversary.