With a cleverness which was almost excruciating, the Aliens had carefully selected a number of animals native to each world, and then constructed robot duplicates. So simple then to place the robots down on a world with a single Director, then wait ... for the humans to inhabit. Naturally the humans screened all the animals and scouted a planet pretty thoroughly before they set up a colony. Naturally their snares and their hunters caught no robots, and never found the deep-buried Alien Director.
Then the humans relaxed and began to make homes, never realizing that in among the animals which gamboled playfully in the trees there was one which did not gambol, but watched. Never once noticing the monkey-like animals or the small thing like a rabbit which was a camera eye, or the thing like a rat which took chemical samples, or the thing like a lizard which cut wires.
The Alien rumbled on through the snow, trembling so much now with ecstasy and anticipation that the suit which bore him almost lost its balance. He very nearly fell over before he stopped trembling, and then he contained himself. In a little while, a very little while, there would be time enough for trembling.
"They could've been here 'til the sun went out," Rush said, "and we never would've known."
"I wonder how much they've found out," Dylan said.
Rush was holding the paw.
"Pretty near everything, I guess. This stuff don't stop at monkeys. Could be any size, any kind ... look, let's get down into camp and tell 'em."
Dylan rose slowly to a kneeling position, peering dazedly out into the far white trees. His mind was turning over and over, around and around, like a roulette wheel. But, at the center of his mind, there was one thought, and it was rising up slowly now, through the waste and waiting of the years. He felt a vague surprise.
"Gettin' kind of dark," he said.