"Fine, I'll tell you. But I have to warn you, Richard, that your question falls under the umbrella of a pseudoscience called xenology. Xenology is an unnatural mixture of science fiction and formal logic. At its core is a flawed assumption - that an alien race would be psychologically human."
"Why flawed?" asked Noonan.
"Because biologists have already been burned attempting to apply human spychology to animals. Earth animals, I note."
"Just a second," said Noonan.
"That's totally different. We're talking about the psychology of intelligent beings."
"True. And that would be just fine, if we knew what intelligence was."
"And we don't?" asked Noonan in surprise.
"Believe it or not, we don't. We usually proceed from a trivial definition: intelligence is the attribute of man that separates his activity from that of the animals. It's a kind of attempt to distinguish the master from his dog, who seems to understand everything but can't speak. However, this trivial definition does lead to wittier ones. They are based on depressing observations of the aforementioned human activity. For example: intelligence is the ability of a living creature to perform pointless or unnatural acts."
"Yes, that's us," agreed Noonan.
"Unfortunately. Or here's a definition-hypothesis. Intelligence is a complex instinct which hasn't yet fully matured. The idea is that instinctive activity is always natural and useful. A million years will pass, the instinct will mature, and we will cease making the mistakes which are probably an integral part of intelligence. And then, if anything in the universe changes, we will happily become extinct - again, precisely because we've lost the art of making mistakes, that is, trying various things not prescribed by a rigid code."
"Somehow this all sounds so ... demeaning."
"All right, then here's another definition - a very lofty and noble one. Intelligence is the ability to harness the powers of the surrounding world without destroying the said world."
Noonan grimaced and shook his head. "No," he said. "That's a bit much ... That's not us. Well, how about the idea that humans, unlike animals, have an overpowering need for knowledge? I've read that somewhere."
"So have I," said Valentine. "But the issue is that man, at least the average man, can easily overcome this need. In my opinion, the need doesn't exist at all. There's a need to understand, but that doesn't require knowledge. The God hypothesis, for example, allows you to have any unparalleled understanding of absolutely everything while knowing absolutely nothing ... Give a man a highly simplified model of the world and interpret every event on the basis of this simple model. This approach requires no knowledge. A few rote formulas, plus some so-called intuition, some so-called practical acumen, and some so-called common sense."
"Wait," said Noonan. He finished his beer and banged the empty stein down on the table. "Don't get off track. Let's put it this way. A man meets an alien. How does each figure out that the other is intelligent?"
"No idea," Valentine said merrily. "All I've read on the subject reduces to a vicious circle. If they are capable of contact, then they are intelligent. And conversely, if they are intelligent, then they are capable of contact. And in general: if an alien creature has the honor of being psychologically human, then it's intelligent. That's how it is, Richard. Read Vonnegut?"
"Damn it," said Noonan. "And here I thought you'd sorted everything out."
"Even a monkey can sort things," observed Valentine.
"No, wait," said Noonan. For some reason, he felt cheated. "But if you don't even know such simple things ... All right, never mind intelligence. Looks like there's no making heas or tails of it. But about the Visit? What do you think about the Visit?"
"Certainly," said Valentine. "Imagine a picnic -"
Noonan jumped. "What did you say?"
"A picnic. Imagine: a forest, a country road, a meadow. A car pulls off the road into the meadow and unloads young men, bottles, picnic baskets, girls, transistor radios, cameras ... A fire is lit, tents are pitched, music is played. And in the morning they leave. The animals, birds, and insects that were watching the whole night in horror crawl out of the their shelters. And what do they see? An oil spill, a gasoline puddle, old spark plugs and oil filters strewn about ... Scattered rags, burntout bulbs, someone has dropped a monkey wrench. The wheels have tracked mud from some godforsaken swamp ... and, of course, there are the remains of the campfire, apple cores, candy wrappers, tins, bottles, someone's handkerchief, someone's penknife, old ragged newspapers, coins, wilted flowers from another meadow ..."
"I get it," said Noonan. "A roadside picnic."
"Exactly. A picnic by the side of some space road. And you ask me whether they'll come back ..."
"Let me have a smoke," said Noonan. "Damn your pseudoscience! Somehow this isn't at all how I envisioned it."
"That's your right," observed Valentine.
"What, you mean they never even noticed us?"
"Why?"
"Or at least they paid no attention."
"I wouldn't get too disappointed if I were you," advised Valentine.
Noonan took a drag, coughed, and threw the cigarette down. "All the same," he said stubbornly. "It couldn't be ... Damn you scientists! Where do you get this disdain for man? Why do you constantly need to put him down?"
"Wait," said Valentine. "Listen. 'you ask: what makes man great?'" he quoted. "'Is it that he re-created nature? That he harnessed forces of almost-cosmic proportions? That in a brief time he has conquered the planet and opened a window onto the universe? No! It is that despite all this, he has survived, and intends to continue doing so.'"
There was silence. Noonan was thinking. "Maybe," he said uncertainly. "Of course, from that point of view ..."
"Don't get so upset," Valentine said kindly. "The picnic is only my hypothesis. And not even a hypothesis, really, but an impression. So-called serious xenologists try to justify interpretations that are much more respectable and flattering to human vanity. For example, that the Visit hasn't happened yet, that the real Visit is yet to come. Some higher intelligence came to Earth and left us containers with samples of their material culture. They expect us to study these samples and make a technological leap, enabling us to send back a signal indicating we're truly ready for contact. How's that?"
"That's much better," said Noonan. "I see that even among the scientists there are decent men."
"Or here's another one. The Visit did take place, but it is by non means over. We're actually in contact as we speak, we just don't know it. The aliens are holed up in the Zones and are carefully studying us, simultaneously preparing us for the 'time of cruel miracles.'"

- Arkady and Boris Strugatsky, Roadside Picnic