"We call it vff," said the alien. "It's - it's hard to describe to a species without vffsense. Imagine trying to describe light to a species that never evolved eyes. But there are forms of life that are only perceptible with vffsense, and they've visited Earth and fed on life as long as it's existed here."
There was a pause.
Then the human said, "That's the worst thing you've ever said."
"Don't worry about it."
"I think I have to, now."
"No, because - well - you have a species of spider which pretends to be an ant, correct? It's not capable of understanding the fact that it's mimicking an ant, but it instinctually mimics an ant in order to deter predators."
"Sure?"
"Humans produce a vff to mimic varths, predators only perceptible through vffsense. The organisms that would like to feed on you are terrified of varths, and so they leave you alone. You aren't aware you do it, you don't have the capacity to understand you're doing it, but you evolved to instinctually do it to deter predators you can't see."
There was a pause.
Then the human said in a very soft and thoughtful voice, "And are there varths on Earth?"
"Yes," said the alien. "Everywhere. But don't worry about it."
"I think I have to, now."
"Well, varths can also sense vff, of course, but to a varth you putting off varth like vff isn't particularly frightening."
"Not frightening, ok. So do they feed on us?"
"No."
"So if not feeding then something... else?"
"Yes. Quite a lot of something else actually."
"What do you mean a lot of something else?"
"Well, you know ostriches?"
"Yeah?"
"When you humans keep ostriches, sometimes you accidentally exhibit features and behaviors that... appeal to an ostrich more than a member of their own species."
"So you're saying varth find us-"
"Incconsivably sexy, desirable to the point they abandon their own home planet and species with some regularity. It's actually quite fascinating, humans are to varth as cats are to catnip."
"Wow that's a lot to take in... you sure know a lot of animal metaphors. You could be a zoologist."
"I am a zoologist"
"Oh?"
"That's why I'm here, talking to you."
"Ah."
