“So what?” Travis snorted quietly. “Well, what about the foxes that’ll need those mice to survive? For want of ten mice, a fox dies. For want of ten foxes a lion starves. For want of a lion, all manner of insects, vultures, infinite billions of life forms are thrown into chaos and destruction. Eventually it all boils down to this: fifty-nine million years later, a caveman, one of a dozen on the entire world, goes hunting wild boar or saber-toothed tiger for food. But you, friend, have stepped on all the tigers in that region. By stepping on one single mouse. So the caveman starves. And the caveman, please note, is not just any expendable man, no! He is an entire future nation. From his loins would have sprung ten sons. From their loins one hundred sons, and thus onward to a civilization. Destroy this one man, and you destroy a race, a people, an entire history of life. It is comparable to slaying some of Adam’s grandchildren. The stomp of your foot, on one mouse, could start an earthquake, the effects of which could shake our earth and destinies down through Time, to their very foundations. With the death of that one caveman, a billion others yet unborn are throttled in the womb. Perhaps Rome never rises on its seven hills. Perhaps Europe is forever a dark forest, and only Asia waxes healthy and teeming. Step on a mouse and you crush the Pyramids. Step on a mouse and you leave your print, like a Grand Canyon, across Eternity. Queen Elizabeth might never be born, Washington might not cross the Delaware, there might never be a United States at all. So be careful. Stay on the Path. Never step off!”

“I see,” said Eckels. “Then it wouldn’t pay for us even to touch the grass?”

“Correct. Crushing certain plants could add up infinitesimally. A little error here would multiply in sixty million years, all out of proportion. Of course maybe our theory is wrong. Maybe Time can’t be changed by us. Or maybe it can be changed only in little subtle ways. A dead mouse here makes an insect imbalance there, a population disproportion later, a bad harvest further on, a depression, mass starvation, and finally, a change in social temperament in far-flung countries. Something much more subtle, like that. Perhaps only a soft breath, a whisper, a hair, pollen on the air, such a slight, slight change that unless you looked close you wouldn’t see it. Who knows? Who really can say he knows? We don’t know. We’re guessing. But until we do know for certain whether our messing around in Time can make a big roar or a little rustle in history, we’re being careful. This Machine, this Path, your clothing and bodies, were sterilized, as you know, before the journey. We wear these oxygen helmets so we can’t introduce our bacteria into an ancient atmosphere.”

“How do we know which animals to shoot?”

“They’re marked with red paint,” said Travis. “Today, before our journey, we sent Lesperance here back with the Machine. He came to this particular era and followed certain animals.”

“Studying them?”

“Right,” said Lesperance. “I track them through their entire existence, noting which of them lives longest. Very few. How many times they mate. Not often. Life’s short. When I find one that’s going to die when a tree falls on him, or one that drowns in a tar pit, I note the exact hour, minute, and second. I shoot a paint bomb. It leaves a red patch on his side. We can’t miss it. Then I correlate our arrival in the Past so that we meet the Monster not more than two minutes before he would have died anyway. This way, we kill only animals with no future, that are never going to mate again. You see how careful we are?”

“But if you come back this morning in Time,” said Eckels eagerly, you must’ve bumped into us, our Safari! How did it turn out? Was it successful? Did all of us get through-alive?”

Travis and Lesperance gave each other a look.

“That’d be a paradox,” said the latter. “Time doesn’t permit that sort of mess-a man meeting himself. When such occasions threaten, Time steps aside. Like an airplane hitting an air pocket. You felt the Machine jump just before we stopped? That was us passing ourselves on the way back to the Future. We saw nothing. There’s no way of telling if this expedition was a success, if we got our monster, or whether all of us–meaning you, Mr. Eckels–got out alive.”

Eckels smiled palely.

“Cut that,” said Travis sharply. “Everyone on his feet!”

They were ready to leave the Machine.