If you had popped into Bruce Foster’s workshop three years ago, you might have found him working on a Charlie Brown “pop-up book” – cutting, folding, taping and gluing pieces of paper to depict, in three dimensions, Chuck’s attempt to kick the football Lucy holds in place, and the inevitable outcome: “Aaugh!”

Last year, you would have found Foster applying the same techniques to a pop-up book showing British actor Hugh Grant entertaining a Hollywood lady of the evening in the front seat of his BMW.

Pop-up books have grown up – fast.

As a result, movable books, invented nearly 800 years ago and still assembled primarily by human hands, are thriving.

After decades of focusing primarily on children’s themes and being viewed by most as a children’s format, pop-up books have entered an era in which anything goes, even – aaugh! – sex. Or as a young couple gasped as they opened “The Pop-up Book of Sex” in the humor aisle of a bookstore, only to have two naked bodies rise up off the page and into their faces: “Oh, my god!”

Foster, one of about a dozen full-time paper engineers in the U.S., passed on the chance to work on that book, but he did tackle his first pop-up book for a mature audience last year: “The Pop-Up Book of Celebrity Meltdowns” was released this year by Melcher Media.

The book recreates – in that in-your-face way only pop-ups can – such embarrassing moments as Janet Jackson’s “wardrobe malfunction” at the Super Bowl, Paris Hilton’s sex video and Michael Jackson dangling his baby boy off the fourth-floor balcony of a Berlin hotel.

“A pop-up book can be a children’s book, but it is certainly not required to be,” said Foster, who lives in Houston and was the paper engineer for “Little Red Riding Hood,” published in 2001, and “Peanuts: A Pop-Up Celebration,” published in 2004.

“I would hope that people would realize that pop-ups are not the exclusive province of children’s books but can be enjoyed by all ages, if sometimes separately.”

In the case of “Celebrity Meltdowns,” he said, “the work we did has brought more laughter to people than any children’s book I’ve been involved in.”

Nicely articulated

This was a good year for pop-up books, said Ann Montanaro.

Having written the book on pop-up books, she ought to know. Montanaro started collecting pop-up books 20 years ago and is the author of “Pop-up and Movable Books: A Bibliography.”

Montanaro said pop-ups are seeing huge print runs this season, including 500,000 copies of “Mommy?” the first pop-up by children’s author Maurice Sendak, and 275,000 copies of Robert Sabuda’s “12 Days of Christmas,” first published 10 years ago.

On top of that, HarperCollins announced that Sabuda, considered the king of pop-ups, would produce a pop-up version of the “Chronicles of Narnia” series.

About 300 new titles come out in pop-up form every year, Montanaro said.

The

Children’s titles still sell far more copies, ranging from about $10 for the “Snappy” series available at Wal-Mart to upward of $40 for some of Sabuda’s books.

Montanaro, director of information technology for Rutgers University libraries, is founder and director of the Movable Book Society, which was formed in 1992. It puts out a quarterly newsletter and holds an international conference every other year.

This year saw a continuation of the trend of pop-ups delving into adult themes, she said.

Montanaro has no problem with that – not even with “The Pop-Up Book of Sex,” which most book stores keep behind the counter.

“The characters are nicely articulated, and they move nicely,” she said. “Actually, it’s pretty awesome.”

Pop-up origins

Movable books date to the 13th century, with the invention of the “volvelle,” or rotating disc. Matthew Paris, a Benedictine monk, is credited with inventing it in 1250, so that circular charts, such as those the monks used to determine when to observe religious holidays, could be read without having to rotate a bulky volume.

Volvelles and lift-up flaps continued to be used in books, but almost always for scholarly purposes. Not until the 18th century were they used to entertain children.

Today, you can find pop-up books on everything from the alphabet to Alfred Hitchcock, from Bible stories to bondage, from Kwanzaa to Kama Sutra, from Smurfs to Stonehenge.

One of this year’s more popular releases was “Graceland, An Interactive Pop-Up Tour.” Readers can tour the various rooms of Elvis Presley’s Memphis, Tenn., mansion, pausing to open his refrigerator, thumb through his albums or change the channels on his TV.

“Graceland,” which re-creates eight rooms in the mansion, was the first pop-up published by Philadelphia-based Quirk Books, whose president is a fan of the tourist attraction.

Melcher Media, meanwhile, released both “The Pop-Up Book of Sex” and “The Pop-Up Book of Celebrity Meltdowns” this year. Those followed “The Pop-up Book of Phobias,” in 1999, and “The Pop-up Book of Nightmares,” in 2001, both written by comedian Gary Greenberg.

“Books must play to their strengths, and one of their strengths is their tactile physical nature,” company president Charles Melcher said. “People don’t snuggle up in bed with a laptop or proudly display their new computer terminal on their coffee table.

“In the digital age, when so much of our info comes to us through a screen, a great pop-up book rekindles that sense of wonder in even the most jaded adult.”