Mammoth

"Sloth. Giant ground sloth."

"Sloth? Like those things that hang in trees? You gotta be—"

"Related," she hissed. "Be quiet. I don't think it sees us."

The thing was turning, ponderously. Way, way up there was a head—it had to be a head, it was at the end of a neck like a tree trunk—that was comically small for its gargantuan body. But small is a relative thing. Matt figured the tree branch it held in its jaws was about the size of his thigh, and it didn't look very big there.

About the time he had that thought, the creature bit through the branch like a toothpick, and spit out the remains. It was facing them now, looking down with big, soft brown eyes that held no fear.

"Let's back away," Susan suggested, in a whisper.

"Good idea."

They began a slow retreat, and the sloth watched them. Then it took a step in their direction.

"Should we run?" Matt asked.

"Best not to, unless we have to," Susan decided. "I figure he could catch us if he wanted to."

The animal took another step, then another... and Matt realized that it was ru

"Run!" Susan hissed. Matt didn't need any prodding. He took half a dozen quick backward steps, afraid to turn away, then he did turn, and ran as fast as he had ever run in his life. Behind him he heard the sloth crashing through brush, and the sound of Susan's footsteps. Wait a minute. Guys didn't run ahead of girls, that just wasn't done. He half turned as he ran, and Susan nearly ran over him. He was so startled that he tripped over his own feet and hit the ground, hard.

"You okay?"

"Ski

They watched the sloth, who seemed to have completely lost interest in them.

"Just scaring us off, I guess," Susan said. "It's so big I'll bet it doesn't have any predators, at least

not when it's full-grown."

"Looks like it could pretty well crush a saber-tooth."

"No kidding. Did you see the size of the claws on that thing?"

"Three on each hand. Long as my arm."

"He's pretty well tearing up that tree."

They watched, from a good distance, as the giant sloth stripped leaves and bark from a tree.

"Wonder why he came after us?" Matt asked.

"Maybe it's a female, maybe there's a cub nearby."

IN the next two hours they encountered a lot of wildlife, though none as dramatically. Several times they saw what looked to be ordinary jackrabbits darting in and out of bushes. Once a wolf regarded them for a while from a distance of a hundred yards, then trotted off. Twice they encountered small herds of deer. They looked like ordinary deer to Matt. He supposed a man who had spent a lot of time with deer in the crosshairs of his rifle might have spotted differences in these animals and modern ones.

He had never hunted. He might have to learn. Could he figure out how to make a useful bow and arrows? A spear? Could he learn to throw it hard and far enough to bring down a swift, alert deer? He suspected he could get mighty hungry while acquiring that skill. Maybe traps would be better. How did one make a rabbit trap?

Stop it, he told himself. Keep a positive attitude. You will figure out how the machine works. We will get out of here. THE sun was still above the horizon when Susan looked around and said this would be a good place to stop. Matt didn't like it.

"You'd be surprised how quickly that will go away," she said. "There's things we need to do, and it's best to be familiar with the immediate area before it gets dark. We need every advantage we can get if there are night-hunting predators around."

Matt still didn't look convinced, so she added, "Do you really want to gather firewood in the dark with saber-tooths prowling around?"

There was plenty of wood lying around, both dead branches blown down by the wind and a couple trees that had been devastated by large herbivores, probably sloths or mammoths. They worked at it for half an hour, and when they were done it was getting harder to see. They arranged a fire and lit it with the lighter they had found in a desk drawer. Soon it was crackling, and Susan's spirits soared with the sparks that leaped into the air. She looked at Matt, who was sweaty, soot-streaked, and gri

"Fire is the basic unit of civilization," he said.

"I never thought of it that way... but you may be right."

"It's the first thing that really set us off from other animals," Matt said. "And it still does. Other animals have languages, other animals use tools. We're still the only animal that manipulates energy."

Susan had felt something like that before, sitting around a campfire. Out in the woods, just you and your family or some other Girl Scouts... you realized that the bad things feared the light, that as long as you were in the light, you were okay. If the fire went out, if the darkness closed in, that was when you were in trouble.

Matt found a few long branches and arranged them with one end in the fire and the other sticking out where they could reach them.

"If we see anything move out there," he said, "grab one of these and throw it toward the movement. Like a torch."

"Good idea."

They ate some of their remaining fruit and a candy bar each.

"Too bad we don't have some—"

"I wish we had some—"

"—hot dogs!" they finished together, and laughed longer than the coincidence really warranted. When they were through with their meager di

"Well, what if somebody finds it? Digs it up, back in the future."

"They'd be mighty puzzled, wouldn't they."

"I mean... would it cause a paradox, or something?"

"I've always operated on the assumption that there are no real paradoxes."

"I don't get your meaning."

"I mean 'real-world' paradoxes. Sure, they can exist in math, and in logic. The human mind can

propose a paradox, but if you examine it you'll find it's either a semantic problem or a hypothetical physical problem that actually doesn't exist in the real world."

"Help me out here."

"Okay. Take a silly paradox, the one Gilbert and Sullivan described in Pirates of Penzance. Frederick was apprenticed to the Pirate King until his twenty-first birthday, not his twenty-first year. But he was born in a leap year, on the twenty-ninth of February. Therefore, though he was twenty-one years old, he had only had five birthdays. You see, the paradox only arises because of the way the contract was worded."

"Got it."

"Then there's another classic one, the grandfather paradox. You build a time machine, go into the past, and kill your grandfather when he's a young boy. So your father is never born, and you are

never born..." He waited.

"So you never built a time machine and never traveled in time and never killed your grandfather."

"Exactly."

"But... that is a paradox. Isn't it?"

"It would be, if time travel was possible. Up to now, I would have sworn it wasn't possible, so I

didn't spend a lot of time worrying about temporal paradoxes."

"Sounds like you'd better reorder your priorities."

"Sounds like."

They were silent for a long time, listening to the crackling of the fire. Susan tried not to look at it, not wanting to destroy her night vision. Once she thought she saw a movement at the edge of their little clearing and she tossed a flaming brand at it. Nothing happened, and the torch soon burned itself out. "So," Matt said at last. "You know any good ghost stories?"

"Matt," she said quietly at one point. "We may never get out of here, right?"