Almost everyone knows the lyrics to at least one song from The Sound of Music. I know a 6-year-old who can even tell the difference between the Mary Martin Broadway soundtrack and the Julie Andrews movie version, which is “inferior” in his opinion. Say what you might about it, The Sound of Music is still a film phenomenon, breaking theater records 35 years after its debut.

What’s different these days, though, is that many audience members show up for screenings dressed like nuns. Others come as Brown Paper Packages or Girls in White Dresses, and there’s always the odd Doe A Deer. One recent fan was a yellow-lycra-suited guy calling himself Ray, a Drop of Golden Sun. And they all sing at the top of their lungs.

Such is the international, audience-participation extravaganza called Sing-A-Long Sound of Music, which concludes its Canadian tour with a two-week run at the Imperial Theatre in Montréal beginning May 24. Think of it as a family-friendly Rocky Horror Picture Show.

“People don’t know what to make of it,” says Canadian promoter Warren Kotler. “They think, ‘Is it a movie, karaoke, or is it a show?’”

It’s all three, and the combination is a commercial blockbuster. Whether you come in costume, to see the costumes, or just to belt out all those memorable songs, this version of the von Trapp tale seems to have something for everyone. Its popularity has surprised even the original promoters in England.

The cinema sensation started in 1999, at London’s Prince Charles Cinema, where it was scheduled for an eight-show run. According to press accounts, demand for tickets was so great that the theater’s answering machine blew up. Bi-weekly shows are still going on. Elton John bought all the seats in the cinema one night for a private party — wimple required.

The Sing-A-Long Sound of Music toured the United Kingdom in 2000, then came to North America, where it has sold out venue after venue. A single show last fall at the Hollywood Bowl drew 18,000. The recent run in Toronto drew upwards of 40,000.

The evening begins with a parade of costumes and a best-costume competition. The emcee — usually a local entertainment personality — winnows the entrants down to around 15, and the winner is chosen according to an “applause-o-meter.” The emcee then leads the audience through a vocal warm-up and explains how to use the items in the provided “Magic Moments Pack.”

For example, everyone in the theater receives a swatch of curtain cloth when they come in. At the point in the film where poor Maria, alone in her room, wonders how she can clothe the kids, everyone in the audience waves their little piece of fabric and yells, “The curtains, Maria! Use the curtains!” As though on cue, she looks at the curtains, and the rest is cinema — and fashion — history. Each kit also contains a plastic edelweiss, for waving during the eponymous song, à la Bic lighters at an Eagles concert.

Then comes the main event: the original 1965 film in glorious, full-screen Technicolor with subtitled musical numbers — the better to sing along with.

Word-of-mouth is really what sells this event, and advance sales in Montréal are picking up as people learn more about it. The draw, Kotler believes, is that “the experience harkens back to an easier time in life. It’s more like vaudeville than theater or a movie.”

And where else is everyone encouraged — nay, expected — to become part of the show?

Those who really want to get into the act come in costume. Leiderhosen abound. One fan went as a gazebo. And there are lots and lots of nuns. Because two genuine nuns actually won contests in England — they were later disqualified — new rules have been created to rout out the real sister acts. Nuns with beards, lipstick, or high heels, or those arriving in limos, generally are assumed to be “civilians.”

Ambitious wannabes might get together with a large group of friends under a big slab of green Astroturf (The Alps). Or figure out how to be Schnitzel with Noodles. (Could be messy.) One of my favorites is the Chinese woman who came to a show in the U.K. as “So Long.” Then there was the man in New York dressed in full Hasidic garb (“A jew, a jew, to you and you and you.”)

“The matinees are more low-key, but evenings are fair game,” Kotler notes. Meaning that’s when a few drag queens and leather guys — dressed as Nazis, of course — are likely to show up, and the crowd may be more tuned in to innuendos in the film’s story. Never mind the falling-in-love part; plenty of sexual tension and dangerous love occur along the way.

A Sound of Music persona is not required for attendance, though. Kotler says only about 20 percent of the audience arrives in costume. Then again, the other 80 percent might be dressed as “Me, A Name I Call Myself.”

The Sing-A-Long Sound of Music will be at Montreal’s Imperial Theatre, 1432 Bleury —just off Ste-Catherine, a couple blocks west of Place des Arts — from May 25 through June 6. For tickets, see www.admission.com, or call 514-790-1245 or 800-361-4595. For more info and photos, see www.singalonga.co.uk.