By Chelsea Lacey-Mabe
COLLEGEVILLE, Pa. (CBS) -- "I thought 'Happy Birthday Courtney' was going to go across the Movie Tavern marquee or something," said Courtney Kilian, who was out celebrating her 40th birthday with friends and family on Saturday when her mother-in-law told her to stop and face the movie theater. "Then the music started."
Playing was "You're the One That I Want," from "Grease," accompanied by a flashmob of dancers from KN Dance and Entertainment. Courtney's husband, Dave arranged the whole thing, knowing the movie would be a perfect theme for his wife's birthday present. And the performance incorporated some choreography from the film, ending with a stroll dance similar to the scene where the cast receives their Rydell High yearbooks.
"Grease has always been one of my favorite movies since I was a little girl and I always sing along anytime I hear one of the songs," said Courtney. "My friend and I saw a flash mob proposal a few years ago and I didn't stop talking about it for days."
Courtney and Dave's kids, Ben and Adam, got in on the surprise too. After the song was over, the boys came running out from behind the performers, holding up "Happy 40th Birthday" signs. Then everyone joined in singing.
Afterwards, Dave breathed a serious sign of relief that the weather had held out. He said the surprise was a group effort that had been months in the making.
"He has done many special things for me over our almost 22 years together, but this definitely takes the cake," said Courtney.
Courtney's birthday flashmob was followed up by dinner with family and friends and blowing out the candles on her birthday cake -- she said fire extinguisher and all.
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