Standing downstage during a performance of Mark Morris’s dance-opera “Layla and Majnun” in the spring, Noah Vinson gazed out beyond the stage. Like the other members of the Mark Morris Dance Group, he was counting musical beats in his head, waiting for his cue to move. Beyond the first rows of seats, he saw only darkness as he looked toward the audience in the Kennedy Center Opera House.

Suddenly, the void was illuminated with a moving spot of light. Vinson recognized it as an usher with a flashlight. “Wow, someone’s coming in really late,” he thought, as his focus was pulled away from the music. Soon, there were more flashlights among the seats. In their glow, Vinson was able to see medical personnel rolling a wheelchair down the aisle. 

He later found out that a man in the orchestra section had become ill and that his wife feared he had suffered a stroke; he was taken to the hospital. The ensuing drama, carried out in whispers, lasted many minutes and drew the attention of patrons throughout the theater. 

From the stage, the dancers were absorbed in it, too, even as they struggled to block out what was happening and keep up with the music.

“You’re trying to maintain composure and do what you have to do, but, you know, what’s going on?” Vinson says. “You make eyes with the other dancers, and you’re all like, ‘What’s going on? Should we stop?’ Everyone was confused and concentrating on what was happening.”

It can seem as though there’s an ocean of separation between the audience in its darkened seats and the performers high up onstage, but is there, really? What do dancers perceive beyond the stage while they’re performing? 

A lot, as it turns out. There’s a dynamic relationship between live performers and the audience. Just as dancers, actors and musicians amuse, provoke or otherwise move their public, the public moves them. Muttering in the seats can be heard onstage. So can the odd argument and ringtones. The sounds and behaviors of spectators can affect dancers’ psychology and even performance quality. They’re energized by cheers, of course, and demoralized when they’re expecting applause or laughter and there’s only silence. But they pick up on far more.

“You hear rustling around, sometimes talking, and coughing, for sure,” Vinson says. “Sometimes there’s that one person who doesn’t have a cough drop. It’s like, ‘Wow, you’re gonna cough during the entire performance?’ ”

Depending on the venue and the choreographic demands, dancers can tell when ticket holders come in late (especially if they’re being guided by flashlights), when they’re dozing and — the worst infraction, many say — when their phones light up because they’re scrolling or texting.

“It makes your heart drop,” says Alexis Evans-Krueger, who dances with Peter Chu’s Las Vegas-based troupe chuthis and with the baroque-burlesque Company XIV in Brooklyn. “ ’Cause you work so hard.”

Dancers say that even small disruptions from the audience can be concentration-busters. When performing, their senses are heightened, and they’re hyper-attuned to what’s happening around them. That’s in addition to the high level of acuity they’ve developed just by being dancers. Body sensation, spatial perception, musical alertness and internalizing other people’s emotions: Much of the dancer’s art depends heavily on awareness.

So just as we are watching them, they are watching us. 

Or at least, feeling us, in one way or another.

“A full house feels warm,” says Justin Metcalf-Burton, a former member of Ballet Arkansas. “You can feel the collective body heat.”

That’s how sold-out “Nutcracker” shows feel. But come February, when ballet companies program “the cool stuff” — by which Metcalf-Burton means the less-marketable premieres and experimental works that dancers get excited about — the smaller audiences can make dancers feel as though they’re “trapped in a paper bag inside a shed, and no one can hear you.”

“The energy of an audience is so palpable,” says Elisa Clark, a former member of Alvin Ailey American Dance Theater and Mark Morris Dance Group. “You can feel when an audience is engaged.  . . . If there are empty seats, you can feel it. People will come offstage saying, ‘It just feels like there’s nobody out there.’ ”

Sensing the mood of the crowd

One of the oldest dance customs has to do with dancers’ perception of the audience — specifically, how it smells. You may have heard that dancers whisper “merde” to one another backstage before they perform, for good luck. Merde is a French word, meaning, to put it politely, manure. Its origins as a dance-friendly form of “break a leg” are unclear, but one account goes back to Paris, where, centuries ago, the stink of horse manure rose when the streets were full of carriages. Likewise, in the theaters, dancers could tell the size of the crowd by its smell; the worse it smelled, the bigger it was. So dancers wished one another “merde” in the hopes they’d encounter a full, fragrant house once they stepped onstage.

Nowadays, does a dancer’s ability to “feel” an audience still stem from sensory cues — heat, chuckles or flashes of motion? Or is it something else?

Michelle Dorrance, a MacArthur Foundation-winning tap dancer and choreographer, says that whether she’s aware of the audience depends on her state of being. When she’s immersed in spontaneous creativity onstage, for example, nothing matters but the music and her instant response.

“If I’m improvising, in my best moments, I’m barely aware. You’re so connected with the musicians that you’ve let go of yourself. But if you’re not satisfied, you can be hyper-aware of every little thing,” Dorrance says. “Whereas if I’m performing something choreographed and it has a very specific emotional arc, I can be really aware of a shift or a presence in the audience.”

Dancers struggle to explain just how they’re able to sense the mood of the crowd in the blackened distance. But whether the audience realizes it or not, most dancers dearly want to spark a relationship.

“When you’re in front of an audience that’s more harsh, you feel that there’s a silence, or a wall that’s put up,” Evans-Krueger says. “And when there’s not, you can feel the audience more with you, like when someone leans in rather than leaning away.” 

This is why silence — not the respectful hush for a tender duet but an unexpected coolness — can be so demoralizing.

“Say you’re doing the ‘Swan Lake’ pas de trois, and you finish the adagio and bow,” says Nicole Graniero, who dances with the Washington Ballet and American Ballet Theatre. “You’d like it if the applause goes on for the variation, but sometimes it dies before you finish bowing. It’s a little bit of a letdown. Not that it makes a difference in the performance.”

She pauses to consider that.

“Wait, maybe it does. I take that back.”

 (Note to self: Clap harder this fall. Clap a lot.)

Graniero points to the emotional lift the cast experiences when the enormously popular Misty Copeland performs with ABT: “When Misty is on, the applause is like you’re in a rock concert.”

Dancers describe a physical rush from an enthusiastic audience. That’s what happened last year at the world premiere of Mark Morris’s evening-length “Pepperland,” a brightly costumed, upbeat tribute to the 50th anniversary of the Beatles’ “Sgt. Pepper’s Lonely Hearts Club Band” album that kicked off in the Beatles’ hometown of Liverpool, England. The cast was nervous until the curtain rose, “and we got a huge ovation even before we started,” Vinson says. 

That kind of reaction is transformative. “You get a surge of adrenaline,” he says. “It definitely helps with the whole energy of the dance. It helps us immediately get into the character and the vibe of the piece.”

Dancers get the best look at their audience during curtain calls, when the house lights often come up. If you’re sitting close to the stage, chances are they’re talking about you as they bow.

That talk, Vinson says, might start with: “ ‘Scoot over a little bit’ or ‘What are we getting for dinner?’ ” Then it might progress to: “ ‘Look at that person; he’s not clapping at all!’ Or, ‘Hey, that one’s really cute!’ ”

There is such a thing as seeing too much, though. That’s the drawback of informal studio performances.

“Those are the most difficult,” Graniero says. “Everyone is very close to you, and you can read their reactions. And you’re trying to portray a certain role, but if there’s no expression on their face, it’s difficult to keep your character up. Are they bored? Are they liking this? My mind starts to wander and think, ‘What are they thinking?’ ”

Being too close for comfort also is the peril of many outdoor venues, before darkness falls, when dancers can clearly see the folks who are slapping away flies or fanning themselves with their programs. These gestures pull the dancers’ focus, and their concentration outdoors is already compromised. After all, they get hotter than anyone, and they’re just as bug-bitten. And, no, they can’t use bug spray. (“We do stuff on the floor and don’t want it to get greasy,” Clark says.)

As for the medical emergency at “Layla and Majnun,” according to the Kennedy Center, the man in question was responsive as he was taken to the hospital. There was no point in stopping the show, says Nancy Umanoff, the Mark Morris executive director, who happened to be sitting near him and raced into the lobby for help. “It doesn’t help the situation. People want to get up and move, and that can impede the medical personnel.” 

Onstage, the dancers did what they always do when something’s going on in the audience: They masked their reactions and carried on. 

“Your perception opens up,” Vinson says. “We knew it was serious, and we had to listen around to maybe get some further direction. So you’re not necessarily listening to the music so much. But we do what we have to do.”