"The whole deal is this," said the robot. "You gotta do exactly like I say — otherwise you're real dead in a hurry. Got it?"

"Got it," said Mishkin. They were strolling a purple plain. The wind was from the east at five miles an hour, and one could hear the electronic sound of birds.

"When I tell you to git down," the robot went on, "you gotta hit the deck fast. There'll be no time for blinking and stumbling. I just hope that your reflexes are in good shape."

"I thought you said it wasn't dangerous here," Mishkin said.

"So, big deal, you've caught me in a contradiction," the robot sneered. "Maybe I had my reasons for lying to you."

"What were they?"

"Maybe I've got my reasons for not telling you," the robot said. "Just listen to what I say now. Hit it!"

Mishkin, too, had heard the faint, high-pitched drone. He threw himself on the grass, bruising his nose in his eagerness to comply. He could see the robot swivelling, two blasters in his metal hands.

"What is it?" Mishkin asked.

"Mating call of the six-legged proto-Brontostegosaurus. When the durned critters are in heat, they'll try to make it with anything."

"Can't they see that I am not an appropriate object for their affections?"

"Sure, but it takes a few minutes for the message to get through to their brains, since the proto-B is not exactly anyone's idea of bright. And in the meantime, you got twenty-three tons of inflamed critter squatting on your head."

"So where is it?" Mishkin asked.

"It's coming," the robot said grimly, twirling the blasters by their trigger guards.

The drone increased in volume and amplitude. Then Mishkin saw something that looked like a butterfly with a six-foot wingspan come fluttering past, droning merrily. It ignored them and went off stage left.

"What was that?" Mishkin asked.

"It sure as hell looked like a butterfly with a six-foot wingspan," the robot said.

"That's what I thought. But you said…"

"Yes, yes, yes," the robot said testily. "It's obvious enough what happened. That butterfly critter has learned how to imitate the mating cry of the proto-B. Mimicry is a commonplace phenomenon throughout the galaxy."

"Commonplace? It took youby surprise."

"What's so surprising about that? It was the first time I ever encountered that butterfly critter."

"You should have known about it," Mishkin said.

"Wrong. I'm programmed only to detect and cope with situations and things that'll be dangerous to humans. That big old flapper couldn't hurt you unless you tried to swallow it, so naturally enough I've got nothing on it in my memory files. You gotta realize that I'm not a goddamned encyclopedia. I deal strictly with dangerous stuff, not with every damned thing that walks or swims or flies or crawls or burrows or however it happens to get around. You get my meaning, son?"

"I get it," Mishkin said. "I suppose you know what you're doing."

"That's what I happen to have been built for," the robot said. "C'mon, let's get on with this promenade."

"I have been having mental difficulties for some time now. I get these ideas, these images. But I don't know what is real and what is not. Sometimes I think that I've eaten and then I find that I have not. Sometimes I think that I have lived and then I find that I have not. I cannot remember why I am here or what crime I stand accused of. Whatever it is, I am sure that I am innocent. I am sure that I am innocent, no matter what I have done."

Mishkin looked up hopefully but found that the jury had recessed, the judge had recessed, the world had recessed, and a bored guard was thumbing through an old issue of Rolling Stone.

Mishkin came to a sudden stop.

"What is it?" the robot asked.

"I see something up ahead."

"Big deal," the robot sneered. "I see plenty of things up ahead. I alwayssee plenty of things up ahead. Christ, everybody alwayssees plenty of things up ahead."

"This thing up ahead seems to be an animal."

"What's so impressive about that?"

The thing that Mishkin saw up ahead was roughly the size and shape of a tiger but with a shorter tail and bigger feet. It was coloured a dappled chocolate with brilliant orange stripes. It looked like a mean, hungry, and unscrupulous hallucination.

"It looks dangerous," Mishkin said.

"That shows how much you know about it," the robot told him. "That there critter is a pachynert, which is an herbivorous beast with a disposition like a cow's, only more timid."

"But the teeth."

"Don't let the teeth fake you out."

"Mimicry?"

"That's it, ace. Now git ahold of yourself and let's move out."

They continued across the purple plain. The robot, not even bothering to draw his blasters, was whistling "Elmer's Tune". Mishkin, walking two steps behind him, was humming "Valse Triste".

The pachynert turned towards them and stared with eyes the colour of coagulated yak's blood. He yawned, revealing incisors like Turkish scimitars. He stretched, showing a smooth ripple of muscle down either flank like sluggish octopi grappling beneath a thin sheet of plastic.

"You're sure he's herbivorous?" Mishkin asked.

"Nothing but grass and dandelions," the robot said. "Although they do appreciate an occasional turnip."

"He looks pretty mean."

"Nature is capable of myriad disguises."

Man and robot came closer to the beast. The pachynert laid back his ears. His tail stood out stiff and straight and high, like the indicator of a dial calibrated for trouble. He stretched out claws like the cruel, curved tines of the devil's pitchfork. He snarled — a sound that prompted several peripatetic trees to close down their branches, pull up their roots, and make for quieter territory on the north forty.

"Nature is overdoing it," Mishkin said. "I could swear that that critter is about to attack us."

"Nature exaggerates," the robot said. "That is the nature of nature."

They were within ten yards of the pachynert, which stood utterly still and gave an excellent imitation of a deadly animal about to charge in a berserk manner and maim and kill any human in sight — and maybe a robot and a couple of trees, too, just for the hell of it.

Mishkin stopped. "Now, look," he said, "there's something wrong about all this. I think…"

"You think too much," the robot said, in a tight, hard voice. "For God's sake, get hold of yourself, man. I am a SPER robot especially trained for this work, and I give you my word that that pitiful cow in tiger's clothing…"

Just then the pachynert charged. One moment it was standing still, the next moment it had burst into a furious rush, claws and teeth gleaming golden in the afternoon glare of the saffron Harmonia sun and its dull, mysterious, little red companion. The beast came with a maximum of verisimilitude, just like a hungry, feral, omnivorous beast who doesn't care what it goes up against, especially if the target is of a manageable size and hasn't got much in the way of claws and teeth.

"Shoo, pachynert, shoo!" the robot called out in an unconvincing voice.

"Hit the deck!" shouted Mishkin.