No suggestion too dirty for cute stars of ‘Puppet Up!’

Brian Henson got to see what a lot of us only imagined.

He would witness what his father, Jim Henson, Frank Oz and other pioneering Muppeteers were up to when the cameras weren’t running.

“They all had a really naughty sense of humor,” he says. “What they would do when the cameras weren’t rolling was so funny, and kind of naughty and blue. Not shockingly, but it was just uncensored basically.”

Anyone else on “The Muppets” set during those moments “found that experience delicious and would all hover around.”

Hence, the answer to the question “What would your father think?” of “Puppet Up!,” the Jim Henson Company’s foray into adult humor.

The blend of puppets and improv comedy played a Las Vegas comedy festival during its formative year of 2006. It went on to become a solid touring attraction and now settles down for an open-ended run at The Venetian.

“This show celebrates this energy I used to see all the time that was never on camera, never recorded,” says Henson, the 52-year-old who now chairs the company founded by his father, who died in 1990.

And if that story doesn’t fully explain the family’s history beyond children’s television, the show itself does. “Puppet Up!” includes two sketches dating to the early ’60s, when they were performed by Jim Henson with his wife, Jane, or with Oz.

The Ed Sullivan-era sketches “points out my dad’s sense of humor was naughty, and shows that this show is an extension of what he started. If people see this show and they just know ‘Sesame Street,’ they’ll go, ‘Oh, that’s kind of a big jump. But if they see the early stuff …”

“Puppet Up!” puts puppets on the hands of a team of improv comics assembled by Patrick Bristow and lets the audience watch the results — either on side screens cropping out the humans or on the stage where the human magic happens.

“We play to a camera. If you want to, you can never look at us,” says Colleen Smith, who came to the cast from Los Angeles’ famed improv troupe The Groundlings. “When things are really complicated or strange, they can look down at the stage and see what the puppeteer is doing.”

Henson says his father never knew improv is taught in classes or that it serves as a training ground for TV and film.

Instead, the senior Henson was always looking for puppeteers who could “ad lib,” his son recalls, never realizing there was a defined means to improve the 1-to-20 ratio of puppeteers who could be funny in the moment.

Years after Jim Henson’s untimely death at age 53, the company was “trying to get a new tone of comedy for puppets,” Brian Henson says. “I had tried to do it with writers and it wasn’t really working.”

The trail led to Bristow, and the workshop results were almost immediately recruited for the Aspen comedy festival. A decade later, the comic sensibility of “Puppet Up!” informs both the Fusion cable news parody “No, You Shut Up!” — where Smith voices “a very conservative Christian squirrel” named Star — and an upcoming R-rated movie, “The Happytime Murders.”

“Puppet Up!” will be a more elaborate production at The Venetian than it was on the road but still relies on audience suggestions to change more than half of its content each night.

“What they give us is what they want to see, and that’s what we give back to them,” Smith says. And, she adds, “You can come to our show very drunk. There’s zero judgment for what you yell out.”

Certain graphic sex acts, for instance, get suggested a lot. The “Puppet Up”-ers don’t shy away from them, nor do they head straight for the deepest dirt.

“I know that’s the hook that gets people in the door, but I actually think that totally sells us short,” Smith says.

“It’s not necessarily filthy. It can be very dark or hyper-intelligent or very ethereal. It can go in any direction. It can also be very mundane. Very slice-of-life, very small comedy coming out of a ferret. You can have a carpool scene with three crazy puppets complaining about traffic.”

But not all of her improv experience carries over so easily.

“The No. 1 rule of human improv is to make eye contact. Because you’re making stuff up on the moment, you really have to watch each other,” Smith says. “To not be able to do that is crazy.”

Or is it? Henson shares what actor-director Jon Favreau told him: “He had a theory that if you engage yourself in another activity, it will free up your subconscious to more speedily improvise.

“He watched us and said, ‘You know what? I think the fact that you’re doing this tough technical thing of working the puppets has actually sped you up as comedians. It’s engaged one half of your brain, which has pulled all the brakes out.”

And that circles back to the other part of what Henson saw his dad and the other Muppet creators doing when the cameras weren’t running.

“That was really where they were developing the characters,” he says. “You can get a sense of it when you watch ‘The Muppets’ … you kind of know Kermit has a very adult side to him, you kind of know Fozzie has some pretty weird perversions.

“Everybody says, ‘Oh the Muppets are so cute and sweet.’ Well, they’re really not.”

Read more from Mike Weatherford at reviewjournal.com. Contact him at mweatherford@reviewjournal.com and follow @Mikeweatherford on Twitter.