So I did the same. 

There was a mark on the wall just next to the hole. I had noted in the light of my flash when I was adjusting the seal. When the lights came on, it was obvious. 

"You notice that, Joe?" I said.

"I notice."

There was a slight, narrow depression in the wall, not very noticeable at all, but there beyond a doubt if you ran your finger over it. It could be noticed for nearly a meter. It was as though someone had scooped out a very shallow sampling of the metal so that the surface was distinctly less smooth than elsewhere.

I said, "We'd better call Computer-Central downstairs."

"If you mean back on Earth, say so," said Joe. "I hate the phony space-talk. In fact, I hate everything about space. That's why I took an Earth-side job-I mean a job on Earth-or what was supposed to be one."

I said patiently, "We'd better call Computer Central back on Earth."

"Oddly enough, I do. And what caused the hole? It wasn't a meteoroid. I never saw one that would leave a perfectly circular hole with no signs of buckling or melting. And I never saw one that left a cylinder behind." He took the cylinder out of his suit pocket and smoothed the dent out of its thin metal, thoughtfully. "Well, what caused the hole?" 

I didn't hesitate. I said, "I don't know." 

"If we report to Computer-Central, they'll ask the question and we'll say we don't know and what will we have gained? Except hassle?" 

"They'll call us, Joe, if we don't call them." 

"Sure. And we won't answer, will we?"

"They'll assume something killed us, Joe, and they'll send up a relief party."

"You know Computer-Central. It will take them two days to decide on that. We'll have something before then and once we have something, we'll call them." 

The internal structure of Computer-Two was not really designed for human occupancy. What was foreseen was the occasional and temporary presence of trouble-shooters. That meant there needed to be room for maneuvering, and there were tools and supplies. 

There weren't any armchairs, though. For that matter, there was no gravitational field, either, or any centrifugal imitation of one. 

We both floated in mid-air, drifting slowly this way or that. Occasionally, one of us touched the wall and gently rebounded. Or else part of one of us overlapped part of the other. 

"Keep your foot out of my mouth," said Joe, and pushed it away violently. It was a mistake because we both began to turn. Of course, that's not how it looked to us. To us, it was the interior of ComputerTwo that was turning, which was most unpleasant, and it took us a while to get relatively motionless again.

We had the theory perfectly worked out in our planet side training, but we were short on practice. A lot short.

By the time we had steadied ourselves, I felt unpleasantly nauseated. You can call it nausea, or astronausea, or space-sickness, but whatever you call it, it's the heaves and it's worse in space than anywhere else, because there's nothing to pull the stuff down. It floats around in a cloud of globules and you don't want to be floating around with it. So I held it back; so did Joe. 

I said, "Joe, it's clearly the computer that's at fault. Let's get at its insides." Anything to get my mind off my insides and let them quiet down. Besides, things weren't moving fast enough. I kept thinking of Computer-Three on its way down the tube; maybe Computer-One and Four by now, too; and thousands of people in space with their lives hanging on what we did. 

Joe looked a little greenish, too, but he said, "First I've got to think. Something got in. It wasn't a meteoroid, because whatever it was chewed a neat hole out of the hull. It wasn't cut out because I didn't find a circle of metal anywhere inside. Did you?" 

"No. But I hadn't thought to look."

"I looked, and it's nowhere in here."

"With the cylinder covering the hole till I pulled it away? A likely thing. Did you see anything come flying out?"

"No."

Joe said, "We may still find it in here, of course, but I doubt it. It was somehow dissolved and something got in." "What something? Whose is it?"

Joe's grin was remarkably ill-natured. "Why do you bother asking questions to which there are no answers? If this was last century, I'd say the Russians had somehow stuck that device onto the outside of Computer-Two-no offense. If it was last century, you'd say it was the Americans."

I decided to be offended. I said, coldly, "We're trying to say something that makes sense this century, losif" giving it an exaggerated Russian pronunciation.

"We'll have to assume some dissident group."

"If so," I said, "we'll have to assume one with a capacity for space flight and with the ability to come up with an unusual device."

Joe said, "Space-flight presents no difficulties, if you can tap into the orbiting Computers illegally-which has been done. As for the cylinder, that may make more sense when it is analyzed back on Earth-downstairs, as you space-buffs would say."

"It doesn't make sense," I said. "Where's the point in trying to disable Computer-Two?"

"As part of a program to cripple space flight."

"Then everyone suffers. The dissidents, too."

"But it get's everyone's attention, doesn't it, and suddenly the cause of whatever-it-is makes news. Or the plan is to just knock out Computer-Two and then threaten to knock out the other three. No real damage, but lots of po tential, and lots of publicity."

He was studying all parts of the interior closely, edging over it square centimeter by square centimeter. "I might suppose the thing was of nonhuman origin."

"Don't be silly."

"You want me to make the case? The cylinder made contact, after which something inside ate away a circle of metal and entered Computer-Two. It crawled over the inside wall eating away a thin layer of metal for some reason. Does that sound like anything of human construction. "

"Not that I know of, but I don't know everything. Even you don't know everything."

Joe ignored that. "So the question is, how did it-whatever it is-get into the computer, which is, after all, reasonably well sealed. It did so quickly, since it knocked out the resealing and air-regeneration capacities almost at once."

"Is that what you're looking for?" I said, pointing.

He tried to stop too quickly and somersaulted backward, crying, "That's it!"

In his excitement, he was thrashing his arms and legs which got him nowhere, of course. I grabbed him and, for a while, we were both trying to exert pushes in uncoordinated directions, which got us nowhere either. Joe called me a few names, but I called him some back and there I had the advantage. I understand English perfectly, better than he does in fact; but his knowledge of Russian is-well, fragmentary would be a kind way of putting it. Bad language in an ununderstood language always sounds very dramatic.

"Here it is," he said, when we finally had sorted ourselves out.

"Where the computer-shielding met the wall, a small circular hole appeared when Joe brushed aside a small cylinder. It was just like the one on the outer hull, but it seemed even thinner. In fact, it seemed to disintegrate when Joe touched it.

"We'd better get into the computer," said Joe.

The computer was a shambles.

Not obviously. I don't mean to say it was like a beam of wood that had been riddled by termites.

In fact, if you looked at the computer casually, you might swear it was intact.

Look closely, though, and some of the chips would be gone. The more closely you looked, the more you realized were gone. Worse, the stores that Computer-Two used in self-repair had dwindled to almost nothing. We kept looking and would discover something else missing.

Joe took the cylinder out of his pouch again and turned it end for end. He said, "I suspect it's after high-grade silicon in particular. I can't say for sure, of course, but my guess is that the sides are mostly aluminum and the flat end is mostly silicon."

I said, "Do you mean the thing is a solar battery?"

"Part of it is. That's how it gets it energy in space; energy to get to Computer-Two, energy to eat a hole into it, energy to-to-I don't know how else to put it. Energy to stay alive." "You call it alive?"

"Why not? Look, Computer-Two can repair itself. It can reject faulty bits of equipment and replace it with working ones, but it needs a supply of spares to work with. Given enough spares of all kinds, it could build a Computer just like itself, when properly programmed-but it needs the supply, so we don't think of it as alive. This object that entered Computer-Two is apparently collecting its own supplies. That's suspiciously lifelike."

"What you're saying," I said, "is that we have here a micro-computer advanced enough to be considered alive."

"I don't honestly know what I'm saying."

"Who on Earth could make such a thing?"

"Who on Earth?"

I made the next discovery. It looked like a stubby pen drifting through the air. I just caught it out of the corner of my eye and it registered as a pen.

In zero-gravity, things will drift out of pockets and float off. There's no way of keeping anything in place unless it is physically confined. You expect pens and coins and anything else that finds an opening to drift wherever the air currents and inertia lead it.

So my mind registered "Pen" and I groped for it absently and, of course, my fingers didn't close on it. Just reaching for something sets up an air current that pushes it away. You have to reach over and sneak behind it with one hand, and then reach for it with the other. Picking up any small object in mid-air is a two-hand operation. 

I turned to look at the object and pay a little more attention to retrieval, then realized that my pen was safely in its pouch. I felt for it and it was there.