"To summarize, the JCB model is intended for rescue work in the Mars colony tunnels. Your task, as usual, is to test the robot in actual field conditions. Do you have any questions?" Susan Calvin's sharp eyes examined the field specialists opposite her.

Powell and Donovan glanced at each other, and then Powell spoke up. "I take it these tests do not involve creating actual emergencies? Should the robot fail, the consequences might not be good." The phrase 'and they always fail at some point' seemed implicit in his words.

"Of course not! The parameters of the field tests are explained in your instructions. Creating actual emergencies? Absurd!" Alfred Lanning snapped impatiently, grey eyebrows bristling.

Donovan raised his hands as if in surrender. "Fine, fine! Just checking. We'll be off".

The pair rose and walked out of the room, Powell closing the door behind them swiftly – though not swiftly enough to drown out the expletive beginning of Donovan's string of complaints.

Lanning snorted and turned to Dr. Calvin. "It seems you were right about teaming them up, Susan. I had my qualms, but they've turned out to be a fine team".

Susan Calvin did not smirk – such facial expressions were not habitual to her – but the slight smile of her thin mouth did have a touch of the self satisfied to it as she remembered her part in the making of the now famous duo.

"I'm telling you, they'll kill each other in a week!" Lanning pounds on the table to emphasize his words.

Susan glares at him in annoyance. "You've been repeating this for ten minutes, and I have told you, time and again, that they will not". She turns to the other person present."Peter, from a research viewpoint, was their work satisfactory?"

Bogert smiles smoothly. "More than satisfactory, in fact it was excellent". His voice becomes oily. "But really, Susan, that's not the point here, is it? The question is whether they would continue to work well together in an isolated environment, such as a field test, and I must say I share Dr. Lanning's concern here".

She sighs, exasperated by her colleagues. "Gentlemen, perhaps we could remember that I am the psychologist here?" She holds up a hand to stop them from speaking. "Robopsychologist, yes, but I am also familiar with the workings of the human mind. As you see, I am content to take your word for it that their engineering work is excellent; perhaps you would be kind enough to take mine that they are more than capable of working together?"

The two men look away from her, abashed.

Lanning meets her eyes and nods. "Very well, if you're sure. Michael Donovan and Gregory Powell are a team".

Donovan looked up as Powell entered their quarters for the Mars testing. His friend didn't seem worried about anything, so he concluded it was safe to assume that JCB-3 had successfully passed the latest test.

Powell tossed Donovan a binder, and sank down into a chair. "Take a look at that, Mike! Perfect results. If this keeps up, we'll be able to send a success report to US Robots in record time!"

Donovan grinned, looking at the robot in question, which had followed Powell and was now standing just outside the door.

"Well done, Jacob. You're doing a great job so far!"

"Thanks, boss. I'm very happy to be performing well." A robot could not, of course, smile, but his voice was certainly pleased. He even seemed to Donovan to have a distinctly jaunty step as he walked across the room to the one adjacent.

Powell had stood up and was gathering things from various cupboards.

"Care for a cheese sandwich, Mike?"

"You're going to make me a sandwich? I'm overcome with emotion!"

"Will you ever grow out of your particularly juvenile brand of humor?"

"Someone has to show a sense of humor around here. But seriously, do make me a sandwich, I'm starving!"

Powell rolled his eyes. "I suppose I'd better, you'll just eat mine otherwise".

"How wise you are, Greg. This is why you're the clever one on the team".

Donovan chuckled at Powell's irritated groan and decided to stop teasing him for the moment, turning to a quick read through of the latest test's report.

A few minutes later, the duo was busily engaged in devouring their sandwiches, while discussing JCB-3's progress.

"I read your report, but I still can't believe it" Donovan remarked.

"Believe what?"

"That we finally have a robot that actually passes field tests, of course! What did you think I meant? That you'd completed a report on your own? That's fairly unbelievable too, of course…"

Powell's stinging retort, though muffled by his full mouth, was perfectly audible. Swallowing, he continued in a more intelligible way.

"Despite your lack of anything resembling wit, you do have a point. I keep expecting Jacob to start running in circles, or develop a religious mania or a penchant for marching around and performing weird dance steps".

"Very true, Greg… I almost wish he would".

"You what?" Powell's eyes were round.

"Sure, it's rather boring when everything works out. I think I'll die of boredom if we don't get a mystery to solve!"

Powell stared at Donovan for a few seconds, then stood up and stalked out of the room, muttering something about insane redheads.

Donovan glared at the cards in his hand. Finally seeming to accept that no amount of hard stares would magically change them, he flung them down on the table. Powell smirked.

"Would you like to stop playing, or do you feel you haven't lost enough yet?"

Donovan swore at him and stood up abruptly, pulling a cigar from his pocket on his way to the door. Still grinning, Powell followed him. The smile, however, slid rather abruptly off his face as he reached the exit.

Robot JCB-3 was walking up and down the corridor. That in itself was odd, but not enough to dismay the two roboticists so thoroughly. No; the cause of that dismay was that the robot seemed to be executing dance steps as he went. Even as they watched, he began – still waving his arms uncoordinatedly in the air – to run in circles.

Powell was the first to find his voice.

"Jacob! What do you think you're doing?"

Jacob stopped immediately.

"I don't understand, boss" he said.

"You were running in circles and dancing! What's the reason for that?" Powell demanded.

"I… cannot explain, boss".

Donovan chose that moment to recover from his stupor.

"What do you mean you can't explain, you tin-can weirdo? You – mmmfff!"He glared at his partner, who had silenced him with his hand.

"I like you better when you're too surprised to talk. Let me deal with this, unless you think you can restrain yourself to sensible questions!"

Donovan pulled a face at him, but nodded and subsided into silence, running nervous hands through his red hair.

"Jacob, you must have a reason for acting like that. You're a sensible fellow; you wouldn't do something for no reason. So come on, tell us what it was".

Jacob, however, was shaking his head, looking distressed. "I can't, boss. I'm sorry, but I can't".

Powell looked at him for a few seconds, then sighed and dismissed the robot, who hurried off down the tunnel. Entering the room, he collapsed into a chair, tugging at his moustache. He glared at Donovan, who was elaborately pantomiming a request for permission to talk.

"Oh, go ahead, Mike. Don't be absurd".

"Thank you kindly, Oh Great One! I apologize for interrupting your magnificent questioning with my foolish words…" started Donovan.

"Oh, shut up! I know I didn't get much out of him, but would you have done any better?" Powell snapped.

Donovan sighed, slumping down in his chair.

"This is a devil of mess, Greg. It's obviously too much to hope for that this is a one-off, so we have yet another malfunctioning robot on our hands. Isn't that just lovely?".

"Hmm, yes. I really should leave you to sort it out alone, since you wanted a mystery so much…"

Donovan winced. "If I ever say something that stupid again, punch me, please".

"With pleasure, my friend, with pleasure".

Over the next few days, the pair began to look more and more harried. Powell seemed determined to pull his mustache out by the roots, while Donovan's hair, never smooth at the best of times, looked as if he was perpetually in a gale.

Jacob continued to dance and run in circles at random moments – though, curiously enough, never while he was performing a field test. Even in those, however, his performance was suffering – at least, that was Donovan's opinion; Powell claimed he was functioning as well as ever. Donovan's sarcastic suggestion that the root of Jacob's malfunctions was an imprinted dislike of redheads earned him a book to the stomach. The truth was both specialists were completely puzzled. The robot's responses to brain-reaction tests were perfect; there was nothing mechanical obviously wrong; yet the undeniable fact was that he was acting very oddly indeed.

One apparent option, often suggested by the colonists who spotted Jacob's strange performances, was simply to order him to stop. Making such a suggestion would earn the unfortunate person a lecture – varying in sharpness and politeness depending on who gave it – to the effect that such an action would only mask the problem, not solve it, and could induce further problems in the robot's mental stability.

Powell and Donovan were in their room, discussing the situation yet again, when someone knocked sharply on the door. They glanced at each other, already resigned to yet another report from one of the colonists.

"Come in" said Powell.

To their surprise, the man who entered was the head of one of the teams that explored the surprisingly vast network of natural underground tunnels. He looked extremely irritated.

"You two are the US Robots men, then?" he said.

"Yes, that's us. How can we help you, Mr…?" replied Powell.

"Lead Explorer Baxter. It's a problem with this new robot of yours; he's been disrupting my work."

"Oh Jupiter, what's that metal screwball done now?" exclaimed Donovan. Powell savagely motioned him to be quiet and offered his own chair to the explorer, perching on his bed.

"My team and I were exploring one of the north-western tunnels. The robot saw us setting off and wanted to tag along, and I saw no harm in it so long as he kept out of our way. Made that very clear to him, too. Everything was going fine, I was thinking about calling the lunch break in half an hour, and suddenly there it is, demanding I call the lunch break now or my men are going to die!" the man sounded indignant.

Powell and Donovan exchanged startled glances. "And what did you do?" Powell asked cautiously.

"Called the damn lunch break, of course. I didn't care to drive the blasted robot madder! I left the men to their lunch and brought it back to you so you can figure out what's wrong with it. It's waiting in the corridor". Baxter turned to leave. At the doorway, he looked back over his shoulder and added a rather belated "Good luck", leaving 'you'll need it' floating, unspoken, in the air.

The roboticists looked at each other in horror. With the slow, halting step of a man who is in hot water up to his neck and knows it, Powell walked to the door and ordered Jacob to enter. Returning to his chair, he stared at the robot who stood in front of him, tugging at his brown moustache.

"Jacob, do you know who the man who brought you here was?" Powell began.

The robot nodded. "Lead Explorer Baxter, boss. I went with his expedition this morning".

"You did a damn sight more than go with his expedition –" Donovan began sharply. Noticing Powell's glare, he continued in a more even tone. "You demanded that lunch break be called or the men would die. Why?"

Jacob's photoelectric eyes glowed. "I was sub listening to the men talk, as I am programmed to do…" The men nodded impatiently; both knew that an important part of the JCB model's function was to 'sub listen' to speech around it, only registering such speech consciously when it gave warning of possible emergencies. Powell waved for the robot to continue.

"One of the men – Explorer García – said that he would die unless Lead Explorer Baxter called lunch break, and the rest agreed. Of course, I couldn't let the men die! That would be unthinkable". He sounded perturbed by the mere idea.

Powell and Donovan looked at each other in a strange mixture of relief and dismay.

"Jacob", Powell seemed to be struggling to keep an even tone, "Have you ever hear of hyperbole? Those men weren't actually going to die, they were just complaining – exaggeratedly, certainly, but just complaining. They – what on Mars is wrong with you, Mike?"

For the last minute, Donovan had looked as if he might have an apoplectic fit. Now, he'd suddenly burst out laughing, a great, hearty bellow of laughter, as if he'd heard the best joke ever. A trained ear, though, would have detected a definite edge of hysteria to his guffaws.

"Nothing, Greg, nothing. I've just solved our mystery, that's all!" He was still laughing, gasping out the words.

Powell's fists were clenched. "Then spit it out, will you? I'd like to share the joke, if you don't mind."

Donovan took a deep breath, sobering up a little. "It's quite simple really. You remember how I made that absurd statement about how I would die if we didn't have a mystery to solve? Well, there you go!" He grinned at the robot. "Well done, Jacob, that was quite a mystery!" With that, he burst into laughter again. Powell stared at him, seemingly frozen with shock.

"Thank you, boss…" Jacob's voice was uncertain. "I didn't mean to cause any trouble…"

Donovan waved him away. "Not your fault, old chap. We'll take it up with US Robots, they'll sort you out. We'll explain to Baxter, too. Go and rest, okay?"

Jacob nodded and walked to the adjacent room, still hesitant. "I really am very sorry…"

"Don't worry about it, Jacob". Powell found his voice at last, though he sounded dazed. The robot vanished through the doorway.

Donovan eyed his friend worriedly. "You okay, Greg? You're not too mad at me, are you? I mean, I'd deserve it, but… "

Powell shook his head. His shoulders were beginning to shake, and his answer came through gusts of laughter. "No, Mike, I'm not. Space knows I should be, but it's just too funny! Do remember though, if you ever say something so infinitely stupid again, I will punch you".

Donovan nodded, chortling. "And I, my friend, will completely deserve it".