By Liam Martin

BOSTON (CBS) — Boston’s comedy whodunit “Shear Madness” is celebrating 40 years of laughs.  It’s the longest-running play in the history of American theater.

The co-creators told WBZ-TV, the keys to its success are its ever-changing script and audience participation.

Bruce Jordan said, “It’s not a play for six actors, it’s a play for seven actors, and the seventh actor is the audience, and they don’t know their lines. And so that keeps everybody on their toes.”

In 1980, he and Marilyn Abrams brought “Shear Madness” to the stage and the laughs have been coming eight times a week ever since.

According to Abrams, the people of Boston really embraced them, and once the show caught on, they kept on coming back.

The script of Boston’s comedy whodunit “Shear Madness” is always changing (Photo Via Shear Madness)

The play is different every night, with the actors improvising and incorporating the day’s headlines into the script.

Actress Celeste Oliva said, “We’re always looking for who’s politically messing up, or is there a funny commercial that’s out, or is there a YouTube video that’s really catching fire, what is the latest teenaged dance craze, or you know, something that’s just very very popular.”

Everyone involved with “Shear Madness” agrees the Charles Playhouse is the perfect location for the production.

Actor Patrick Shea said, “Every audience member can see every other audience member, so when they participate they are sometimes communicating with each other, disagreeing with each other. It’s just the perfect space for it.”

The actors never know what to expect, making the show fun and scary and crazy all at the same time.