The last man to discover an alien life-form

Magro looked across the greensward. It always reminded him of home, and it was hard to remember that this wasn't Earth, that the plants beneath his feet weren't grass, and that the trees in the distance were wholly foreign.  Amongst the trees stood one of the enigmatic buildings with which the expedition had become familiar: a cylinder of silvery metal, somewhat higher than a man, capped with a dome, without any visible windows or doors. None of the humanoid beings who inhabited this planet was currently in sight.
   As well as feeling nostalgic, Magro felt depressed. They had been on this planet for almost a hundred of its days, and yet they had discovered nothing useful at all; about how its climate might change with the seasons, about its ecology and geology, about its wildlife (if any), and least of all about its inhabitants. After endless tests, the air was finally recognised as breathable and the crew had been able to remove their helmets. But the water from the streams and the fruit on the trees were still out of bounds: they contained no obvious poisons, but there were chemicals which it was feared might cause stomach disorders. Then there were the inhabitants ......
   The crew had met them soon after landing, but were yet to make any meaningful contact with them. Someone had christened them the "Noids", for they looked distinctly humanoid. They were about the same height as humans, and they were entirely hairless. It was impossible to distinguish betweeen men and women, and there were never any children on view. They all dressed alike, in a simple shift reaching to the feet, so they gave the impression of gliding as they moved. They had ever been heard talking to each other.
   Infuriatingly, they showed no interest in making contact with their visitors. They ignored the spaceship entirely, and when they encountered the crew they bowed slightly and then moved on. They appeared to walk around randomly, in ones and twos, never in groups. They were never heard to utter a sound, and were never seen eating or drinking. Whatever did these strange people do? Magro wondered, for perhaps the hundredth time.
   Azarin, one of the crew, came running towards him. "I've just discovered something!" he called, gabbling in his excitement. "I saw one of the Noids entering a cylinder!"
   "Go on!"
   "Yes! He walked up to it, and suddenly a door opened and in he went! And I looked, but I couldn't see any sign of a door at all! So I sat outside for ages, waiting for him to emerge, but he never did. What do you think's going on?"
   "How can I say? For all we know, it could just be a lavatory! They aren't very big, those cylinders: no room for more than two or three people inside."
   "No. Unless, of course, they contain steps going down underground".
   At this point Telemar, the commander of the mission, who must have been listening to the conversation after approaching unobserved, intervened to say, "Has it occurred to you that all this has been set up for our benefit? A scenario very close to life on earth has been specially created here; only they haven't got it quite right.
   "Consider: the air is breatheable, but contains too many rare gases. The water has trace elements that make it unsafe to drink. These plants under our feet look like grass, but they aren't. The fruit on the trees could be eaten, but the chances are that you'd be spending a long time on the toilet afterwards. Then again: there aren't any animals or birds. There aren't even any insects! I haven't seen an insect. Have you? And as for the Noids... have you never suspected that they might be robots? They aren't the slightest bit interested in our spaceship. Can you imagine chimpanzees, or even cattle, completely ignoring a strange new object that suddenly appeared in their territory?
   "So: whoever might be in charge of this planet: how are they doing this? and even more importatly, why?" 
   "We could try forcing some truth out of them!" Azarin said.
   "How?"
   "Well, we could kidnap one of the Noids. We wouldn't hurt him: just take his clothes off, perhaps, and see what he'd got underneath. Anyway: make him communicate. Or we could blast our way into one of the cylinders. Or perhaps ignore the Noids entirely, set up the heavy digging equipment, and see if there's anything useful to be had here".
   Telemar shook his head. "No; for a variety of reasons. Firstly, because, as you well know, we're strictly forbidden to use violence towards indigenous inhabitants unless we're in serious danger. Which at the moment, we're not; though we might be if we followed your suggestions. Whoever set up this ridiculous planet for us must be extremely intelligent; extremely powerful. Who knows what might follow if we started to get aggressive? Intergalactic war maybe?"
   "Well,have you any bright ideas?" Magro asked.
   "None at all. And in any case, we'll be leaving this planet soon enough."
   "Leaving? whatever for? are we running out of food, or what?"
   "Yes, but there's more to it than that. You don't understand the politics of it. Voyages like this are fantastically expensive. It was made clear that this was our last shot, and if we didn't discover something really profitable, that would be it. Even the food for the trip was cut back, to save money, so we can't stay here much longer even if we wanted to. And what's happened? We've discovered a planet that makes no sense, inhabited by creatures (if they are really creatures!) which make even less sense. So we'll go home having achieved precisely nothing. And that will be that. Goodbye to any further explorations". 
 Magro looked across the grass that wasn't grass, through the trees that weren't trees. The spaceship stood there, shining and silent and redundant.