When you watch The Dark Knight or Interstellar or Serenity, the footsteps you hear aren’t Christian Bale’s or Matthew McConaughey’s or Nathan Fillion’s. Those footsteps belong to Alyson Dee Moore, or to one of her partners at the Warner Brothers Sound Foley stage in Burbank, California.

Moore is a Foley artist, and whether you know it or not, you’ve definitely heard her work. She’s contributed to films like The Dark Knight, Interstellar, Inside Out, Big Hero 6, Serenity and about 260 other projects, including television shows and video games like Halo 5: Guardians. Much of Moore’s work, particularly in the realm of science fiction and fantasy, comes down to making realistic, believable sounds for objects, places and characters that don’t exist in our world. As you can imagine, that takes a lot of creativity and some seriously outside-of-the-box thinking.

History of Foley

In 1927, the first talkie, called The Jazz Singer, swept the nation and revolutionized movies. Unfortunately, Universal Studios didn’t get the memo — they’d just completed Show Boat, which was to be a silent retelling of the Broadway musical.

It was destined to be a flop. Audiences wanted synched voices and sound, not soundtracks set to otherwise silent scenes. They needed to find a way to save the picture, to liven it up with some sound. Enter: Jack Foley.

Foley, who was working as a sound effe at Universal Studios at the time, came up with the idea of projecting the film onto a large screen in a sound stage and then using all manner of props and people to create the sounds that should exist in the world of the movie. With his method, they transformed Show Boat from a silent picture into something that had a prayer of competing against The Jazz Singer.

Foley didn’t just change Show Boat, though — he invented an entire industry. Following Show Boat, Foley’s method became a standard practice for adding post-production sound effects direct-to-picture thereafter. Foley’s name has stuck with the process ever since.

What Is Foley?

Though film sound is perhaps at its most successful when everything feels like it’s been recorded right there in the world of the film, the vast majority of what we hear when we watch films doesn’t come from the production track (the sound recorded by microphones on set or on location), but from sound stages and studios after the fact in the form of ADR (Automated Dialogue Replacement), ambient sound effects (think room or background noise), library effects (explosions, engine noises, airplanes, etc.) and Foley, or performed sound elements.

Sometimes called “Foley walkers,” a big part of the work of a Foley artist is replacing or creating footsteps for scenes. Moore and the other Foley artists at WB Sound replace every footstep in every project, even if the production tracks are clear. A lot of this comes down to consistency — Moore and her Foley partner will often divide characters between them to guarantee that a character’s footsteps sound the same every time they appear onscreen. All told, that’s a lot of footstep work.

Foley artists do a lot more than footsteps, though — they’re responsible for creating the sounds that make scenes sound dynamic and real, even when the sounds in question are the stuff of fiction.

Writing With Sound

Moore describes foley work as a marriage between sound editors and foley artists. Because film sound comes from a number of different places, the lines between effects rendered by Foley artists and those cut by sound effects editors can be blurry and shifting. It’s a constant collaboration, and one that requires a lot of trial and error to produce the perfect sonic signatures for elements in the film.

For live-action projects, production tracks might be able to provide guidelines for realistic sounds that need to be cut and added in with the crisp clarity that only Foley artists can provide. But when it comes to animation and video game projects, things get really interesting, because they’re mostly on their own.

Moore’s worked on a number of animated features, like Pixar’s Inside Out and Frozen. When it comes to projects like that, there’s a lot of thinking involved about how things should sound when there’s no real or practical yardstick within the film itself.

“There’s no production track,” says Moore, “so you’re coming up with sounds that sound real even when they aren’t.”

Things get even weirder in video game projects, where Foley artists are often given pictures and illustrations of characters in order to create realistic in-game sounds. A lot of the decision-making around those sounds comes down to material. In Halo 5: Guardians, for example, the characters often have shields, weapons and armor. There are scales and metals and plastics, and each of those materials requires different treatment from Foley artists.

Foley stages are intentionally filled with all kinds of seemingly arbitrary objects. Often it’s those objects used together, banged on different materials or layered among several other tracks, that produce the exact sounds that Foley artists, sound editors, sound supervisors and directors are looking for.

For Halo, Moore used things like staple guns and wrenches to get the metallic sounds created by heavily armored characters with massive footfalls and big weapons. For Transformers, she used a 10-pound rock to create the footsteps of those big machines on surfaces like cement, dirt and grass. As for Frenzy, the little metal character in Transformers? “That’s a metal hand mixer and a whisk,” she revealed.

In addition to the smattering of objects, Foley stages have sections of floor dedicated to a number of different materials and surfaces, largely for footstep work. Ever wonder how they make it sound like characters are walking on the metal surfaces of big metal ships floating in space when the actors are standing on soundstage floors and sets?

“We actually have a surface called ‘spaceship,’” Moore says. She describes it as a piece of metal that’s not “too ringy” but has cement and metallic sound that feels deep and solid and believable as a part of a space-faring vessel.

Things Aren’t As They Seem And It’s Awesome

Perhaps one of the most fundamental truths of Foley work is that nothing is as it seems. You may not have ever heard Christian Bale’s footsteps. The sounds of his hands on the steering wheel of the Batmobile weren’t made by him at all. Transformers ambulate to the sound of controlled crashing rocks, and E.T.’s movements are courtesy of jello and a t-shirt.

“Don’t look at what I’m using, or you’ll hear that,” says Moore. It’s true — once you know the truth behind something, you can sometimes hear the elements and common objects that make up fictional elements in film. But unless you know, there’s a certain magic and mystery to hearing sounds we’ve never heard before created by objects that might be in your room, office, garage or fridge.

Take, for example, Moore’s work on the 2000 film Red Planet.

“When we were doing the film “Red Planet” they wanted the sound of walking on Mars, but it needed to be something spongy and crusty” says Moore, “a sound that we’ve never heard before. We tried walking on sand, both wet and dry for the crusty part, and on a wet chamois cloth for the spongy sound. Nothing was working.”

It was a big ask, trying to create the surface of Mars, but after some trial and error, fate lent a hand.

“I went to get something out of the crappy refridgerator that was in the coffee room and there was a large, untouched, bowl of jello that I had made a week earlier for the 25th Anniversary DVD of E.T.,” says Moore. “When they had done the film originally they had used jello in a tee shirt to make the sound of E.T.’s movements when he was walking around, but we never used it so there it sat and because it was such a crappy refrigerator, it had developed a thin layer of ice on top.

“I pressed my hand gently on it,” says Moore, “and lo and behold, that is the sound we used for the footsteps. I did the sound wild with my hand and the editor cut it in as a sweetner for the footsteps.”

Foley Is About Making Things Sound Real, Even When They’re Not

A lot of what we hear in science fiction — the pew-pews of blasters, the ambient hums of space ships, the roaring of engines — comes from libraries. Those sounds are often layered to create distinct sound signatures for fictional objects, and to give us the feeling that we’re in a galaxy far, far away.

The work of Foley artists is, to some degree, about balance. The sounds that come from Foley stages are often fundamentally real and are largely based on a person’s interaction with their environment — footsteps on the ground (even if that ground belongs to another planet), running a fingers down the cover of a book, hands on a steering wheel, a key in an ignition.

Those sounds anchor us to something we recognize and can understand, even if much of the world in the film is unfamiliar and fantastical. In a sense, those sounds are what connect our world to the ones we enter in fiction, making them feel more real and more impactful.

Sometimes, it isn’t the off-the-wall sounds that make a film or television show or video game feel vast and believable. Instead, it’s the sounds that we hear and recognize from our own world that transport us.