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Not very long ago, I came across a letter from a woman somewhere in the press. She is absolutely convinced that UFOs exist, but that all of them are manufactured on Earth by ordinary people at secret factories. Where does such a strange conviction come from? Once, when she was just a little girl, she saw a 'saucer' hovering in the forest over a lake and managed to get so close to it that she could examine the hull. The hull was assembled with our earthly hex-head bolts. To her, the thought that super-advanced civilizations could use such a purely earthly anachronism as bolts seems far too incredible.
She is absolutely right. Nowhere in Cosmos would it ever cross anyone's mind to assemble the hulls of spacecraft with bolts. What she saw is indeed not a product of super-advanced civilizations.
But the funniest thing is that not a single earthly design bureau would ever risk assembling the hull of an aircraft—or any other vehicle, for that matter—with bolts. This was exactly what she, not being a specialist, did not know. The hull is a load-bearing structure, and assembling it with bolts means exposing the pilot to deadly danger, since during a hard landing, the bolts can be shorn off, and then the hull will collapse like a house of cards, snapping shut like a mousetrap on both the crew and the passengers. Here on Earth, we use welding in such cases, and if the parts cannot be welded, we use rivets which, when bucked, fill the entire hole, keeping them from being shorn off even during the hardest landing.
Perhaps we possess some other new technologies, but bolts... even for us, this is old hat from the century before last, since under vibrations, threaded connections happen to unscrew on their own. Assembling a bridge over a river with bolts is fine, but as for the body of an automobile—that is highly questionable. This was known even in pre-revolutionary Russia, which is why the hulls of marine vessels back then were already made with rivets (though today it is welding).
So, what did that woman actually see? A common imitation. Those bolts were never screwed in by anyone, and no one will ever unscrew them, because they are molded as a single whole with the hull—just like the nuts on the wheels of plastic toy cars. There might be a steering wheel inside, a tank, and headlights, all looking exactly like the real thing. But... it is a toy.

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For a long time now, all the ufologists on Earth are perplexed by why the aliens make such a strange choice of candidates, whom they 'took for a ride and returned.' People of science, people seriously studying the paranormal, and even simply people with a higher education—let alone two—are invited to ride on a flying saucer extremely rarely. On the other hand, people with below-average intelligence and children are the favorite passengers.
Everything is correct. Such passengers may be more or less observant, but they will easily swallow any nonsense about anything they are told. But just try explaining to a graduate of a physics and technology institute what kind of fuel a saucer runs on when it… has no engine at all, and other things in that same vein. That's why here, in the sky above us, UFOs are scurrying around, invitingly blinking their lights, flying yet unable to fly.

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