Sound effects editors assemble the noises that bring viewers into the physical world of a movie or TV show, whether it's the meaty sound of a fistfight or the ear-shattering roar of a T. rex. They're more important than many people realize—after all, sound is half of the viewer experience. Mental Floss spoke with three of these sound magicians to learn about creating the illusion of reality, going undercover to capture sound, and when a trip to the grocery story is sometimes necessary.

1. THEY DON’T JUST MAKE THINGS GO BOOM.

The phrase “sound effects” may conjure up thoughts of explosion-packed action movies or the buzzing and clashing of light sabers. But sound effects editors don't always work on noises that dramatic. “It can be as subtle as crickets,” says Ric Schnupp, a New York-based sound editor and mixer. “[Sound effects] can be super detailed or super huge.” Heather Gross, a sound effects editor on films such as Into the Woods (2014) and TV's Quantico, adds that this fact can sometimes be lost on the average person. “If something isn’t exploding they don’t think of it as an effect,” she says. “Those birds, the car that drove by in the background, all these mundane things that always surround us—people don’t think about them in life and they certainly don’t think about it when they’re watching something.” But these small sounds are still a crucial part of a sound effects editor’s job, helping to create the reality onscreen.

2. THEY’RE OPPORTUNISTS.

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Sound effects editors are highly attuned to their environments and ready to capture unique sounds at a moment’s notice. Fortunately, sound recording equipment has become so small and portable that an editor can carry a high-quality recorder with them at all times. That's handy, since some sounds you hear all the time in life are actually pretty difficult to find in a sound library. Gross, for example, says she's always ready with her recorder whenever an opportunity presents itself. “There are life things that you are always thinking about recording. Any time someone has a baby, I record the baby,” she explains. And while attending a recent U. S. Open tennis match, she didn’t lose a chance to capture crowd sounds: “That sort of crowd, you can’t fake that,” she says. “You’re never in a situation where you can get 10,000 extras to do crowd reaction.”

The small size of some modern sound recording equipment also makes it possible to collect sounds without attracting a lot of attention. Schnupp calls his portable setup “incredibly covert.” “It’s a little thing that looks like an iPhone," he says "so it’s very easy for me to look like I’m checking my email, when in fact I’m getting sound.”

3. THEY’RE LIBRARY PATRONS …

But not the regular kind of library. Capturing live sound adds authenticity to sound design, but sometimes it's much more time and cost-effective to use sound effects from an established commercial library instead. Case in point: Schnupp relates a story about working on a forthcoming documentary that needed the sound of women screaming at a rock concert, and making the decision to purchase a sound library specifically for that purpose. “I’m not going to go spend $100 for a concert ticket and try to sneak in mics that I’m not allowed to have,” he explains.

While a sound studio will typically purchase the rights to several sound effects libraries, individual sound effects editors often also amass their own personal libraries based on recordings they’ve done, giving them the ability to draw on multiple resources.

4. THEY HEAR THE WORLD DIFFERENTLY THAN MOST PEOPLE.

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Whether due to natural inclination or years of practice, sound effects editors have a sharper sense of hearing than most of us, and a more imaginative way of listening to common sounds. Schnupp recounts sitting on an airplane while the stewardesses ran through safety protocols, and noticing that “that little seat buckle thing” evoked the metallic click of a gun. He somehow convinced the stewardess to give him the buckle. “I brought it into the studio and we used it for a ton of different shows and films ... When someone holds the gun up like they’re going to shoot someone and you hear a little ‘click click’ sound ... We use that for everything and everyone loves it.”

5. ONE PERSON’S JUNK IS ANOTHER PERSON’S SOUND EFFECTS GOLDMINE.

Schnupp says the studio where he works contains a number of physical objects used to create sound effects. This includes slabs of marble and tile surfaces for recording footsteps as well as wooden boxes and palettes that imitate the hollow sound of porches, docks, or boardwalks. Schnupp says that the studio also contains “a large pile of props that we use to make sounds. It’s sitting in the corner and we kind of look like hoarders.” In the pile: bins of different shoes, paper articles, ceramics, metal objects, and broken toys.

Using objects of this sort to create footsteps and other sounds falls more properly under the role of a Foley artist, whose responsibility is to create sounds intimately associated with onscreen characters—like the rustling of clothing or sound of setting down a coffee cup. There is a fine line between Foley and sound effects work, however, and depending on a project’s budget a single person might assume both roles.

6. THEY MIGHT HAVE TO MUTILATE A (DEAD) CHICKEN.

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Speaking of unique ways sound effects editors work their magic—horror movies sometimes require resorting to techniques almost as gross as the content of the film. Schnupp says that one of the best ways to mimic the sound of ripping flesh is to buy a raw chicken at the supermarket and tear it apart. “If you really want it to sound real, sometimes it’s got to be actual flesh,” he explains.

Of course, there are ways of imitating the sound of breaking bones that might not make a vegetarian wince. “Celery is really good for bone breaks,” Schnupp says.

7. THEY SWAP SOUNDS.

Sound effects editors not only pull from commercial and personal libraries, but sometimes borrow from the personal libraries of other sound effects editors. As with many creative disciplines, the people in the sound effects field are both familiar with one another’s work and willing to help one another out. If a particular sound effect is missing, it can be helpful to think about sounds heard in the work of colleagues and to ask around. Roland Vajs, a sound editor and mixer known for his work on Green Room (2015), says he’s typically happy to share and that there’s no point in being stingy with sound effects since editors will alter them to fit their project anyway. “It’s what you do with the sound,” he says, “not what sounds you have.”

8. THEY HATE LOUD NOISES.

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Along with heightened sound sensitivity, some sound effects editors have an aversion to loud or jarring noises. “Most sound editors hate noise and hate loud music,” says Vajs. “I am always covering my ears.” One of Vajs’s peeves is cavernous restaurants with concrete walls that amplify sound—an effect that a good sound mixer on a film would seek to avoid.

9. THEY LEND PERSONALITY TO INANIMATE OBJECTS.

Sound effects editors are not just concerned with sound effect accuracy—they also aim to strike the right tone and mood. According to Gross, automobile sounds in particular are more than just noise. “If you have a specific car or a car that is a character, then you always want to get your own library,” she says. For the Sophia Coppola film Somewhere (2010), which prominently features a Ferrari, she and her colleagues created a library of sounds recorded while performing various maneuvers in a Ferrari (tough job, but someone's got to do it).

10. THEY PLAY ON YOUR PSYCHE.

While audience members may be conscious of everything they see unfolding on screen, sound can work on a more subconscious level. Vajs argues that because sound is more abstract than visual information, it has the power to heighten emotion by working on a more intuitive, less literal level—it can “subtly influence how the viewer perceives the film,” he explains. “Psychology is always involved.”

Schnupp agrees, particularly when it comes to horror movies. “The sound is what makes you scared ... and that’s why it’s so crucial,” he says. “It can make a huge impact in horror, perhaps more so than in any other genre.”

11. EVERY SOUND IS THERE FOR A REASON.

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From stray background noises to gunfights to subtle sounds, everything that the audience hears in a film or TV show has been put in place with intent. “Every single sound is there for a reason,” Schnupp says. “Nothing is by accident ... And even if something was there by accident it would never make it through the final mix.”

Many people, however, may not realize the extent to which soundscapes in film and TV are constructed. “Maybe 90 percent of what they’re watching has been replaced,” Gross says. “But if we’ve done our jobs well you can’t detect it.”