At a recent conference in England, a group of fully-grown adults played a strange game of telephone. They sat quietly, passing papers down the line, each person working quickly but carefully. But the strangest part wasn’t that adults were playing a children’s game, or that they were writing instead of whispering. It’s that they weren’t using real languages.

These people have invented their own languages, called conlangs, and this game is actually a test. Each person’s task is simple: Translate a passage from another person’s conlang into their own, then pass it along. The last person translates it back to English. If the text is the same then they’ve all passed the test. Otherwise, as in childhood telephone, they end up with ridiculous results.

Fantasy movies and TV shows are increasingly enlisting conlangers to invent languages as part of the effort to build more immersive fantasy worlds. Historically, though, conlangs haven’t been so popular. The Ewoks in Star Wars spoke in silly nonsense noises, but today, fully fleshed out conlangs are all but essential for blockbuster movies like Avatar and hit TV shows like Game of Thrones.

Producers like David Benioff and Dan Weiss, executive producers for Game of Thrones, have said that conlangs add depth to characters and quite simply sound more realistic than the nonsense noises featured in older films and TV shows.

Linguists agree. “I think you can tell the difference,” says Arika Okrent, a trained psycholinguist — someone who studies the psychology of language — and author of In the Land of Invented Languages. She says you have to listen closely to what the characters are saying, but that you can tell when the noises are just nonsense.

And she’s not alone. David Peterson, one of the only conlangers to parlay the hobby into a profession, says he agrees. Even as a child, he says he knew that the alien languages in Star Wars made no sense. Today, Peterson is well known for the languages he has invented for shows like Game of Thrones and Defiance, as well as for films like Thor: The Dark World.

But Okrent says it’s possible that only certain people, like trained linguists, can notice right away. Okrent and Peterson may be more attuned to how languages sound because they study them in depth, and are therefore uniquely able to distinguish conlangs and real languages from nonsense.