How well did the audience play its part? The reviews are mixed.

Ally Rzesa/Globe Staff

Whether they realize it or not, audiences essentially function as supporting characters at the plays or musicals they attend.

Because of the up-close-and-personal nature of live performance, their collective personality is often a key ingredient in the atmosphere generated by any given production, part of theater’s mysterious chemistry.

“This is a conversation that I have a lot with other actors,” actor Sharmake Yusuf told me. “The audience is an integral part of the theater experience. The audience is equally as important as any scene partner. You need to be reacting to what they’re giving you.”

Of course, what they give actors can be good or bad. I’ve recently witnessed both kinds of audience impact.

Good: The joyously enthusiastic young audience at a Nov. 9 student matinee of “Roald Dahl’s Matilda the Musical" at Wheelock Family Theatre at Boston University.

Ranging from third-graders to high school seniors, and hailing from half a dozen different schools, they had the 632-seat theater rocking.

The subject matter had obvious appeal and points of identification for them — they were students watching a show about students, after all. But it was impressive how attentive and responsive — the ideal combination — they were throughout the 2½-hour show. They seemed to consider themselves virtually part of the action, with a stake in how things unfolded onstage.

So they lustily booed the villain, tyrannical headmistress Miss Trunchbull, and howled with glee when Matilda ultimately got the better of her and Miss Trunchbull fled up the aisles and out the theater’s door. At the curtain call, the students leaped to their feet to deliver a well-deserved standing ovation to 11-year-old Erin Grimm, who played Matilda.

Emily Ranii, who helmed “Matilda” and is Wheelock’s artistic director, told me that audiences “certainly” can be seen as a kind of supporting character. She cited another student matinee of “Matilda” when audience members reached out their hands to high-five child actors as they ran down the aisles in one scene.

When an audience is fully engaged like that with a production, said Ranii, “You can definitely feel the energy in the room. It’s like the difference between flat soda and effervescent, sparkly champagne."

Actors have to be ready to respond to either flavor — and to unpredictable circumstances. Which brings me to the bad.

At a recent performance of “The Chinese Lady" at Central Square Theater, a dozen adult spectators, in several different groups of three or four, strolled in five to 10 minutes late. This, in a show that only runs 90 minutes.

The location of their seats required them to pass right in front of the play’s two actors, no more than 10 feet away from them, a conspicuous distraction just as the actors were establishing their onstage rhythm. An intricate one-act drama like “The Chinese Lady” needs a delicate, nuanced balance and an air of intimacy to succeed. We’re not talking “Mamma Mia!" here. An actor’s concentration is vital, and those Central Square latecomers risked disrupting that.

It’s a credit to the professionalism of actors Sophorl Ngin and Jae Woo that they did not let the late arrivals diminish their excellent performances. But c’mon, people. Actors have a tough job. Don’t make it tougher.

An audience can be the fuel that inspires performers to greater heights, or the cold water that makes them wish they’d gone to law school instead. (Of course, some productions absolutely deserve the chilly response they get.)

“My favorite audiences are vocal," said Yusuf, who won an Elliot Norton Award this year from the Boston Theater Critics Association for his performance in SpeakEasy Stage Company’s production of “BLKS," by Aziza Barnes. “I love when there’s no doubt from the jump that the audience is engaged with us in telling the story."

Sharmarke Yusuf (right), shown with Thomika Marie Bridwell in SpeakEasy Stage Company's "BLKS," says his "favorite audiences are vocal."Nile Scott Studios

But one gets the sense that actors and audiences are still getting reacquainted, more than a year after live performance resumed.

A certain amount of rust on both sides of the footlights was inevitable, given that theater came to a screeching halt in March 2020 because of the COVID pandemic and didn’t fully resume until September 2021. When they returned to the stage, actors found themselves performing for people whose faces they could not see.

“At pre-pandemic performances, there was more of a communal feeling," said Yusuf. “You could see the faces and hear the responses of people around you. It sort of let you know how they’re taking in the show."

“With the masks, there was a cut-off, a physical and metaphorical barrier between the audience and you,” he added. “So much of how we communicate is through our face. Not having that in the audience, it felt that we were sort of on our own. To me the actor-audience relationship is the most important aspect of theater. We rehearse a show for weeks, but everything changes when you do it for an audience.”

Though it may seem paradoxical, the bond between actor and audience can tighten when something goes awry onstage — if the actor is quick-witted enough. I saw Paul Melendy improvise his way out of a jam two weeks ago during his virtuosic solo performance as Ichabod Crane and other characters in Greater Boston Stage Company’s “The Legend of Sleepy Hollow.”

At a key juncture near the end of the play, Melendy is supposed to light a candle. At that performance, he struck one match, then another, then another. Nothing. As moments passed and things grew more and more awkward, Melendy suddenly broke the tension (and the fourth wall) by beseeching, in a high-pitched, desperate voice: “Won’t somebody help that man?"

That device — channeling the voice and viewpoint of the audience, commenting on the action while enacting it — is one that stand-up comedian Jim Gaffigan has honed to an art form. The “Sleepy Hollow” audience laughed at Melendy’s ad lib, and the actor abandoned his attempt to light the candle. Then, in the last scene of the show, Melendy faced the audience from center stage, holding aloft the still-unlit candle — and elaborately pretended to blow it out. More laughter. Melendy had made allies of the audience, enlisting them as supporting characters in a literal sense.

Sometimes, of course, an audience can inject itself into a performance in ways that are not … helpful.

Renowned Boston actor Paula Plum experienced a bizarre moment in 2014 when she portrayed Linda Loman, wife of Willy Loman, in a Lyric Stage Company production of Arthur Miller’s “Death of a Salesman." At the end of one Sunday matinee, Plum walked across the stage for what was supposed to be a solemn, heart-rending scene: a gathering at Willy’s graveside.

But as Plum passed an elderly patron in the front row, the patron — for whom the play’s title had apparently not been enough of a hint — exclaimed loudly: “Did he die?”

By e-mail, Plum said: “It was an effort to effect the grief-stricken widow for the rest of the show!”

The most direct and successful use of the audience as supporting characters I’ve seen lately occurred, ironically enough, at the same Central Square Theater performance of “The Chinese Lady” that was marred by late-arriving spectators.

Lloyd Suh’s play is inspired by the true story of Afong Moy, who was brought from China to New York in 1834 at age 14 and put on display in a museum. Ngin, as Afong, addresses her remarks to us, the people in the seats, essentially thrusting us into the roles of the 19th-century spectators who gawked at Afong, implicating us in her cruel exploitation.

Then, near the end of the performance, director Sarah Shin takes it a step further with a savvy bit of staging not called for in Suh’s script. Ngin strides rapidly upstage and forcefully tears down a set of hanging white curtains. There stands a large, circular mirror, in which we can see ourselves. We are forced to watch ourselves watching. It’s a queasy feeling, given the context.

Over the next month-plus, Boston-area theaters will try to fill seats with holiday shows or prepare to launch the second half of the 2022/2023 season in January. While some theaters have eased mask mandates, COVID is not over, and its specter continues to keep many seats empty.

“We are still learning new audience behavior," Wheelock’s Ranii said. “Audiences are buying tickets later than ever. There’s that mentality around staying nimble and flexible. We were inside for so long, and people are choosier about what they choose to do."

Given that reality, Ranni said, “Theaters need to create reasons for audiences to show up, to come out of their shells and be in communion with each other.”

And with a lot of actors, for they, too, are eager for that kind of communion.