Swan watched closely, pointing out a line of wolves on the bank downstream, snagging drowned caribou calves with their teeth and dragging them in teams back up out of the water. It was only at that point that the river ran with ribbons of red.

“Will the wolves cross too?” Wahram asked.

“I don’t know. In the terraria they often would, but the streams aren’t as big as this. You know—you see it inside a terrarium and it’s great, but this is different. I wonder if they think so too. I mean, they’ve done this a lot, but always looking up at the land. They’ve never been out under the sky. I wonder what they think of the sky! Don’t you wonder?”

“Hmm,” Wahram said, considering it. Even to him the sight of the Terran sky was almost inconceivably odd. “It must look strange. They must have a sense of space, they’re migrating creatures, after all. They migrate in the terraria. So they must know this is different. From the inside of a cylinder to the outside of a sphere—no, if they feel that—” He shook his head.

“I think they seem more panicked than usual. More wild.”

“Maybe so. How are we ourselves going to get across?”

“We swim! No, not really. Our aerogels will work as rafts, we’ll float across. If we’re lucky!”

She led him down to the ford, where the scent of the caribou was strong, and strips of fur eddied in the shallows. The wind poured through him, and he could feel his lungs etched as cold shapes, pulsing and alive. “Come on,” she said, “we have to get out of here before the wolves get here to clean up on the poor dead babies.”

“All right, but show me how.”

“Your mattress is your raft, we each have one. It’s kind of like a coracle of aerogel, so it’s hard to see but you’ll float in it fine. If you tip over you have to hold on to it, or else swim fast.”

“I’ll hope not to tip over.”

“That’s for sure! This water is freezing. Here, take this branch to paddle. I think the thing to do is to walk out as far as you’re comfortable, then get in and let yourself be taken downstream, and paddle when you can for the far shore. We don’t need to be in any hurry, because the first curve of the river downstream will put us over near the other side anyway. And you’ll feel it when you’re over the shallows on the other side. Follow me, you’ll see.”

So he did; but he bounced on the water, and his raft felt too small, and the deepest part of the current swept him by Swan, who was laughing at him; then he paddled hard. She caught up with him, paddling in circles, and shouted to him, “Put your head under the water!”

“No!” he exclaimed indignantly, but she laughed and shouted back, “Put at least one ear under the water, you have to hear it! Listen to it underwater!”

And she leaned out from her coracle and ducked her head under for a few moments, then pulled out sputtering and laughing. “Try it!” she commanded. “You haveto hear!”

So gingerly he leaned out and stuck his right ear under the dancing surface of the water, holding his breath, and was astonished to find that he had immersed himself in a loud electric clicking utterly unlike anything he had heard before in his life. He pulled his ear out, heard the rush of the world, then stuck his whole head back in, holding his breath, and heard with both ears that electrifying clicking and clacking sound, which must have been the sound of stones rolling hard over the river bottom, thrown along by the rapid current.

He pulled out, blowing like a walrus. Swan was laughing at him and shaking her head like a dog. “How’s that for music!” she shouted. Then Wahram’s coracle scraped the shallows on the other side and he jumped out, but tripped and fell. He was just able to grab the little raft as he splashed and clambered to his feet, then sloshed up to dry land. Not elegant at all, but he was still alive, and his bodysuit kept him dry and warm—now thatwas the technological sublime. And they were on the far shore.

Swan found a high point above the river and pitched their tent just before dark. The tent was a single big shell, transparent and bouncy on transparent tent poles. Their rafts would serve as their beds. They sat outside the door of the tent and Swan cooked them first a soup made from powder, then pasta with a pesto and Gorgonzola sauce. Finally chocolates for dessert, and a little flask of cognac.

It was still twilight when they were done, though the sun had set an hour before. The tent flapped in the wind, and the immense sluicing of the river over its rocks rumbled up out of the ground and filled the air. They had been going for eighteen hours straight, and when Swan said, “Time for bed,” Wahram nodded and yawned. The sleeping bags she pulled from their backpacks were also aerogels and resembled the mattress rafts, as well as their tent material, and for that matter the bubbles they had drifted down in—all aerogels, hard to see, light, squishy, warm. “But we’ll still be cold unless we sleep together,” Swan said, crawling into his bag beside him and pulling both bags over them.

“Ah yes,” Wahram said. “I’m sure.”

In the semidarkness he could afford a smile. She kissed him, though, and caught him in the act.

“What,” she said.

“Nothing.”

She rolled onto him, and their combined weight caused his back to touch the ground under his mattress. It was a chill touch and he had to mention it. “We may have to stay side to side.”

“Hell no,” Swan said, and squiggled out of the bag. “Here, get up a second, let’s put my bag under the mattress. That should do it.”

It did. By then they were cold. She got the top of his bag over them properly and climbed onto him, shivering; and after a tight hug she shifted around and started kissing him again. Her mouth was warm. She was a good kisser, passionate and playful. Her penis, so much littler than his, was nevertheless poking his belly, feeling something like a belt buckle gone awry. He too was fully aroused, and getting happier by the second.

Now it was said that their particular combination of genders was the perfect match, a complete experience, “the double lock and key,” all possible pleasures at once; but Wahram had always found it rather complicated. As with most wombmen, his little vagina was located far enough down in his pubic hair that his own erection blocked access to it; the best way to engage there once he was aroused was for the one with the big vagina to slide down onto the big penis most of the way, then lean out but also back in, in a somewhat acrobatic move for both partners. Then with luck the little join could be made, and the double lock and key accomplished, after which the usual movements would work perfectly well, and some fancier back-and-forths also.

Swan turned out to be perfectly adept at the join, and after that she laughed and kissed him again. They warmed up pretty fast.

Lists (14)

A round mound made of big irregular boulders, interleaved together small and large to make an almost smooth cone at Mercury’s north pole

Flat rocks laid in circles, one layer on the next, each layer bigger for a few layers, then the same for two or three, then smaller, slowly, up to a rounded point, so that it looked like a big pinecone of rock

One big boulder topped by gold, melting in the brightside crossing onto the rubble plain below it

Another boulder, encased in stainless steel, not melting

Another, rubbed with cinnarbar

Patterned gaps in the ground filled with liquid copper

Shards attached to a knobby headland so that it looked like a cactus