Charlie Jane Anders is the author of The City in the Middle of the Night , out on Feb. 12. Here, she investigates one of the most unsettling images in the long history of sci-fi, a “what if?” scenario that she also factors into the new novel.

Science fiction is full of sickening ideas, like body snatchers and alien parasites and mind-controlling earworms. But one of the most skin-crawling tropes in science fiction is also probably pretty realistic: humans eating alien life forms that later turn out to be intelligent.

The most famous iteration of this storyline is probably the Futurama episode “The Problem With Popplers,” in which an addictively delicious snack food turns out to be the children of the Omicronians — who are understandably pissed about people eating their babies. There’s also one part of George R.R. Martin’s novel-in-stories, Tuf Voyaging, where a group of colonists eats delicious “mudpots,” not realizing they’re a sapient species.

According to TV Tropes’ exhaustive cataloguing of this gruesome story idea, Terry Pratchett’s Discworld also digs into the notion. And Joanna Russ’ comedic story “Useful Phrases for the Tourist” teaches interstellar travelers to say, “Are you edible?” and “I am not edible.” In Douglas Adams’ Restaurant at the End of the Universe, the sentient Dish of the Day is not only sentient, but urges people to eat it. Then, of course, there’s the first season of Star Trek: Discovery, in which the Terran emperor, Philippa Georgiou, knowingly eats a Kelpien, one of poor Commander Saru’s relatives.

This is all on my mind because — minor spoiler — sapient-eating also happens in my new novel, The City in the Middle of the Night: Human colonists eat the indigenous life forms on the planet January, not realizing they’re a highly advanced civilization.

And when humans aren’t trying to eat aliens that we don’t realize are intelligent, of course, the aliens are frequently trying to eat us. Which is why To Serve Man is a cookbook.

This trope isn’t nearly as common in science fiction as humans and aliens having sex, for obvious reasons — it’s a lot more disturbing, with its implications of cannibalism. (Especially compared to hooking up with aliens who look like supermodels or pop stars with just a little colorful body paint.)

But if we ever do manage to find life on other planets, I imagine us doing the same thing we’ve done with almost every other life form on Earth: trying to eat it. Particularly if humans colonize a planet that already supports life and then suffer a food shortage, leading to a widespread famine, the colonists will almost certainly hunt for meat to supplement their diet.

In The City in the Middle of the Night, humans have colonized the tidally locked planet January, and centuries later, our descendants are barely holding on with inadequate food sources. Some plucky humans venture into the planet’s night side, to hunt the large, furry creatures who live there, whom human beings call “crocodiles.” But the novel’s protagonist, Sophie, learns early on that the crocodiles are actually an advanced life form called the Gelet — and humans just haven’t been able to communicate with them until now.

The realization that humans have been hunting, butchering, and eating January’s indigenous intelligent species is a horrifying one, and this fact also makes it harder for people to accept that the Gelet are really sapient. After all, nobody wants to admit that they’ve been eating people, and the whole concept is kind of sickening. But on the other hand, because the Gelet are large and scary-looking, and humans have only interacted with them in narrow circumstances, it’s easy to see why people think they’re just like cows, or maybe elks.

“It’s the basic human instinct of ‘survival of the piggiest,’” Patric M. Verrone, the writer of the Futurama episode about Popplers, tells me. “The crew was hungry” in that episode, says Verrone, so when Leela checks “that thing on my wrist” and discovers the only edible life form on the planet isn’t poisonous, her team becomes addicted to these delicious fried-shrimp-like critters. But Leela does feel guilty for “eating them by the bucketful” when she discovers they’re the offspring of an intelligent species, says Verrone.

“I think if we met aliens in real life, and they were intelligent, we would not immediately eat them,” Verrone adds. “At least I wouldn’t. Especially if they’re prepared with cilantro.”

Novelist and game designer Jim Munroe, having incorporated a people-eating-intelligent-creatures storyline into his novel Angry Young Spaceman, complicates the trope in his new graphic novel in progress, Zeroed Out. The book finds Earth in a “galactic supply chain,” and one of the rules is that “the acceptability of eating meat is related to intelligence differential,” says Munroe. So in this future, humans are allowed to eat chickens and fish, but not beef or pork. But the “offworlders” who work with humans are smarter than us, so they are allowed to eat beef and pork — and these super-intelligent aliens “are nuts for bacon.”

Lately, I’ve been having lots of conversations with Star Wars fans about the porgs, those adorable bird creatures in The Last Jedi whom Chewbacca tries to roast over an open fire. Are the porgs intelligent? Or just too cute to eat? They certainly figure out that the meal Chewbacca is preparing is one of them. But they don’t seem to be able to communicate — or if they do, it’s as unintelligible as Chewbacca himself. StormMiguel Florez, a Star Wars fan who stars in the short film A Murder of Porgs, says, “They’re definitely smarter than chickens. But it’s hard to tell if they’re as smart as humans.”

The real question is: How do we tell if a creature is intelligent, if it communicates differently from us? And how intelligent does a creature have to be before it’s “off limits”? We can’t even define intelligence in any meaningful way, let alone come up with rules for which creatures are too smart (or too purposeful) to eat.

We’re already asking these questions about some creatures on Earth. Most people agree that dolphins are too intelligent to eat, and we go out of our way to eat dolphin-safe tuna. Some people also argue that squids and other cephalopods are too smart for us to eat. And then there are cows, which have been shown in some experiments to be able to learn, and to have emotional intelligence.

A few years ago, BBC Radio 4 did a four-part series called Would You Eat an Alien? in which host Christine Nicol talked to a number of philosophers, bioethicists, and animal experts about the ethical debate. What emerges is a clear difficulty in figuring out how intelligent and social a creature is, and how much harm will be done by eating them — especially with an alien life form that you’ve just encountered for the first time.

The final episode of the series, “Alien Persons,” grapples with the question of whether a creature is a thing or a person, and thus deserving of rights. On the one hand, philosopher Roger Scruton argues that only humans think of our lives as a story, with a narrative arc that can be brought to completion. On the other, veterinarian James Yeates says that pretty much anything you can point to as special about humans also exists somewhere in the animal realm. Is personhood a matter of autonomy? Or the ability to make plans? Language use?

Perhaps aliens only achieve personhood if they have their own sense of right and wrong. If we can prove that an alien creature has its own moral code, argues Scruton, “then we must be prepared to attribute to it the rights that we claim against it.”

(Be warned: Would You Eat An Alien? has kind of a heartbreaking ending.)

Science fiction has long wrestled with the question of how to tell if a creature is intelligent, or capable of communicating. In H. Beam Piper’s Hugo-nominated 1962 novel Little Fuzzy, a prospector named Jack Holloway discovers an adorable species of furry creatures called Fuzzies. He thinks it’s a thoughtful, emotional species, but an evil corporation wants to exploit the Fuzzies’ home planet. Holloway has to go to court to prove the Fuzzies are sapient, and not just merely smart animals.

Then there’s The Word for World is Forest by Ursula K. Le Guin, in which humans enslave a planet’s indigenous “creechers,” on the grounds that they’re not really human-equivalent ... until the “creechers” prove otherwise. The reverse occurs in several stories in which humans are placed into a “zoo” by advanced aliens, and can only win their freedom by proving their intelligence to their captors. Proving intelligence turns out to be remarkably difficult when you’re dealing with a species that thinks very differently from the way you do — and maybe only looks at humans the way we look at pigs or cows.

Science fiction history reflects a hard truth: We, as a species, tend to eat first and do complex behavioral research much later. And we’re not particularly good at making on-the-spot assessments of other creatures’ claims to personhood — especially when we get hungry.