Kristen Stewart's Love Lies Bleeding Costar Breaks Down Their Sex Scenes: 'So Not Glamorous' (Exclusive)

Katy O'Brian admits sex scenes are awkward.

The breakout Love Lies Bleeding actress — a former police officer and competitive bodybuilder who grew up in Indiana — shares intimate onscreen moments with costars Kristen Stewart and Dave Franco in the film.

In interviews with PEOPLE, O'Brian and director Rose Glass (also known for the 2019 horror Saint Maud) reveal the not-so-sexy work that goes into making a sex scene.

"It's just so not glamorous, and it's really not that sexy when you're doing it. I mean, first of all, you've got a boom-mic guy that's got his microphone hovering over you while it's all happening," jokes O'Brian.

Adds Glass, "It is all quite unsexy, to be honest."

Everything is agreed upon beforehand

Well before cameras start rolling, the actors, in conjunction with an intimacy coordinator, outline exactly what they're comfortable with and how it'll be choreographed. (Christine McHugh and Rebekah Wiggins are credited as intimacy coordinators on the project.)

"There are nudity riders and stuff," says Glass. "Basically it's literally agreed in writing before anyone even gets on set exactly what isn't going to be shown: from what angle, how much, how little. By the time you get there, it is all quite mechanical."

O'Brian explains that there's no room for improvising.

"We stick with the script for those scenes, because with intimate scenes there's massive approvals that go into everything," she says. "If anything changes, we have to go back and sign more paperwork. We just had to approve it all ahead of time."

They get creative with buffers to separate actors

Not only are there "modesty garments," which are "always kind of funny, weird panty-liner-looking things," according to Glass, but other materials are used to shield private parts.

O'Brian says they used "a lot of tape" down there for Love Lies Bleeding.

"Our intimacy coordinator wanted to make sure I had lots of layers between me and Kristen, so she would tape down one layer of fabric, especially in our first bedroom scene, where you have to see the side of me, so we can't have underwear on."

"Then," recalls O'Brian, "I think there was another layer, and there was literally a cut-out yoga mat that she put over me, and taped that down."

The actress says she was given a hockey cup to use at times, and that Franco, for their sex scene, was given a "deflated yoga ball to use as a buffer" between them.

"There was some funny little experimenting with protection," she says with a laugh, adding, "It just felt really not sexy and very silly."

The elements can get in the way on set

Love Lies Bleeding was filmed in New Mexico, where the heat would make the cast sweaty and grimy at times.

O'Brian recalls one mishap caused by the heat when she had to pull down her "tiny shorts" for a sex scene and the taped-down buffer (which felt like "wearing a diaper," she says) slid off.

"It was so hot that every time Kristen would pull the pants off, everything would just pull right off. So finally we're just like, 'Can we just do this with one layer? Do we really need a diaper?' " recalls O'Brian.

"We're filming in Albuquerque. It's hot, it's in the summer — it's like 112 degrees. So we feel sweaty and gross, and we just hope that we're not stinky and everything," she adds. "It doesn't feel as sexy in the moment."

The cast and crew's minds are usually on anything but sex

Everyone on set has a job to do, and for the most part each cast and crew member is most preoccupied with cameras, microphones, angles and choreography.

"You're usually worrying more about something like the camera falling on the actors and killing them and hoping that doesn't happen, and forgetting the fact that, oh yeah, they're simulating sex," jokes director Glass.

One scene, for instance, was filmed in a "teeny weeny" bathroom on a handheld camera, shot in a "really long take," according to Glass.

Describing the camera operator who was filming with the handheld, Glass says, "Poor guy was just standing there probably with his arms about to fall off. Even though he's got these beautiful women making out and 'having sex' in front of him, he's like, 'No, please make them stop. My arms hurt!' "

Love Lies Bleeding is in theaters now.