Director Ferne Pearlstein's quest to explore Holocaust humor took more than a decade to happen. Here's why.

It took some foul-mouthed comics to convince Ferne Pearlstein her “Last Laugh” project was ready for its closeup.

The filmmaker had wanted to shoot a documentary about humor and the Holocaust for some time. Since 1993, to be exact. That’s when she read a college paper on the subject.

“I was so young in my career. I felt like I needed to grow more as a filmmaker,” Pearlstein says. And even when “Life Is Beautiful” rocked the Academy Awards in 1998 she held her ground.

“It opened the doors to the new conversation about it. We needed to see how it developed over time,” she says of the movie that used humor in a daring fashion.

Then she watched the 2005 documentary “The Aristocrats.” That film chronicled some of comedy’s biggest stars telling versions of one very bawdy joke.

“I knew people were ready,” she says.

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Filmmaker Ferne Pearlstein

If only it were that simple. A helpful donor came along in 2011, but the project demanded more than financing. Plus, the comedy culture kept shifting under her feet.

“How society reacts to satire has evolved so much since then,” she says. That’s putting it mildly. There’s little mild about her documentary.

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“The Last Laugh” examines how humor helped some Jewish prisoners in the Nazi concentration camps. We meet several survivors who recall the gallows humor that sprang from the very worst conditions imaginable.

“If you were funny before the camps you were funny in the camps. It’s who you are,” one person says in the film.

“The Last Laugh” also explores the very nature of challenging comedy. Gilbert Gottfried, Rob Reiner, Jeffrey Ross, Sarah Silverman and Mel Brooks weigh in on the subject. It took time to assemble that rich cast. In fact, the documentary scheduled an interview with comic legend Joan Rivers, but the icon passed before the shoot could happen.

All the while, fresh news events made the subject even more complicated, like the terror attacks on the French magazine Charlie Hebdo which killed 12 people.

FAST FACT: Ferne Pearlstein’s husband, Robert Edwards, directed the 2016 Christopher Walken film “One More Time.”

That doesn’t mean comedians lined up to appear in the movie.

“Nobody says yes on the first go around,” she notes, although Rivers ironically was the first celebrity to agree to be interviewed. Other voices, like Larry David, were included via existing film footage. Each star had his or her own reason to participate … or decline.

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“Larry David didn’t want to intellectualize about the concept,” she says. His longtime collaborator, director Larry Charles, proved just the opposite.

The film’s emotional through line is Renee, an Auschwitz survivor with with joy in her heart.

“She has an incredible sense of humor … she finds the positive in life. [But] she doesn’t think everything is funny. Everybody has different lines,” she says.

Even Brooks, whose “Springtime for Hitler” faux musical remains one of comedy’s most daring moments. Just ask him what he thinks of “Life Is Beautiful” … and be ready to wince.

“The Last Laugh” isn’t for the casual comedy fan. The documentary delves into some of the darkest stories about life in concentration camps. And not every survivor cares to joke about it. Understandably so.

The assembled comedians, though, took the concept seriously.

“Nobody was holding back if they agreed to be in the film,” she says. One topic not directly discussed in the film? Political correctness. And yet the subject came up behind the scenes.

She asked Reiner if he would repeat some of the words uttered during his landmark 1970s TV show “All in the Family.”

He politely refused.

“I’ll get completely ostracized,” he told her.

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“Here’s a show that was a long time ago. Now, you can’t even say [those words] now as a an example,” she says.

Another dangerous element to modern comedy has nothing to do with the content. It’s the context, she says. If a YouTuber shoots part of a stand-up’s routine and edits it down to a single phrase the meaning can be lost. Or, much worse, changed entirely. And then there’s the comedian telling the jokes in the first place.

“The question of who can tell a joke is very important,” she says.

Directing “The Last Laugh” had a lasting impact on Pearlstein.

“Renee and her daughter have become like family members to me,” she says. “To be able to have such open and honest conversations with Renee, who lived what she lived through, we’ve gotten so close we can talk about anything.”

“The Last Laugh” opens at Laemmle Theaters in La March 16.