Nick made sure that he had multiple lines of defense against sunlight. If he nodded off, he didn't want to wake up scorched or irradiated. The best defense would be to keep enlarging his underground shelter and getting away from the opening to the surface, but Nick needed a rest.

He pulled out Petra's display and started tapping through menus, checking to see whether the alien device had figured out any more English. It had. There were new menu options called Charging, Copy, and Discharging, and Nick tapped on Charging curiously. That pulled up a list of mostly gibberish, but aluminum, iron, and copper were in the list, in that order. Are these all elements?

The amounts of everything were set to zero. Nick selected iron. Nothing further happened, so he took one of the iron cubes he had made and put it to the input port. Petra promptly consumed it, and the amount of iron jumped to 35. Nothing came out, however. Where is she putting it? Nick wondered, not for the first time. Can she get full, or will she store an arbitrary amount of stuff?

He tried Discharging next, and iron was the only entry in that list. When he selected it, Petra printed out a chunk of iron. Interestingly, it came out as a rod with two ends and six sides. Each end was in the shape of a hexagon. So that's your default, huh? Nick couldn't think of anything to do with that information, so he just shrugged. Aliens.

Seeing Copy made Nick hopeful. He selected it, and nothing happened. He tilted Petra and poured a precious few drops of water into her input port. The display acted up for a few moments, then presented a line of gibberish letters followed by Confirm (Y/N)? Taking a chance, Nick typed Y.

An ingredients list appeared, and it had only two entries, each with zero amount. Nick's jaw dropped, and then he grinned. I need to find some hydrogen and oxygen, I guess? There's oxygen in the air, because I'm breathing. Sure enough, the amount of the second ingredient ticked up to one unit after a few moments. Nick labeled that one oxygen, and the other one hydrogen, hoping that he was getting it right.

He picked up a piece of rock he had cut and offered it to Petra. To his surprise, Petra consumed the rock completely, and the oxygen level went up. Nick blinked, confused. A rock made completely of oxygen? What? Nick peered at the walls around him. There were different kinds of stone in them. Nick tried a few bits of each kind that he saw. Petra kept eating them and the oxygen number kept going up, but no hydrogen.

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Well, crap. Where am I going to get hydrogen from, then?

Nick leaned back against a stone wall and stared at the alien device that had given him a chance. He spoke aloud for the first time in hours. “Petra, I'm gonna need some help here. I need water.” He opened up the bottle he was working through and took a few more swallows, then forced himself to stop and put the cap back on.

“How smart are you, anyway? Are you, like, a person? Or are you just really awesome software?”

Nick shifted position slightly and frowned. He hadn't expected an answer, but he had to try lots of things that sounded stupid. It was the only way to hit whatever was going on in alien brains when they thought this thing up.

He gently hit his head against the stone behind him a few times. “Okay, stupid shit that makes no sense, coming right up.” He called up the Search box and typed HELP. Nothing happened. He tried a few dozen other words with no effect.

Then he tried typing Search into the Search box, which called up a different Search box. Only instead of a keyboard with letters, this box had the list of materials. Nick stared at it for a little while. Do you understand now what “search” means, Petra?

Nick selected hydrogen and pressed Enter.

For a split-second, he thought he felt something. Then most of Petra's display lit up with a drawing. Petra was in the center of it. A body was next to it, exactly the size, shape and position of Nick himself. All of the groceries were visible too, along with the chair and carpet. Nick tried scrolling and it worked, then pinched to zoom out. A blob that was probably the car showed up in the image. The outline didn't really match, but then, neither did the car any more, the way he had cut into it.

A dashed line cut across the bottom of the image. It seemed to follow the outline of the foxhole, only about fifteen feet below it. Frowning, Nick picked up Petra and moved her back and forth. The image might be shifting. Nick zoomed back in, and did it again. Now the image was definitely moving.

It's live, and centered on Petra at all times. Nick scrolled until the dashed line was visible, and moved Petra again. The dashed line also moved. When Nick held Petra all the way in, at the spot where he had dug the farthest north, the very edge of the dashed line lit up in one place.

Nick stared. Petra is scanning for hydrogen, and she found some deeper in!

He stared at the wall of solid rock between him and what he needed to make water. I guess I'm doing a lot more digging tonight. The relief hit Nick hard, and he sagged back in the chair. He closed his eyes, just for a moment...