"SO YOU THINK YOU CAN DANCE" Choreographers and judges perform on the season finale. Pictured L-R: Tyce Diorio, Mia Michaels, Nigel Lythgoe, Mary Murphy, Adam Shankman and Debbie Allen. Photo Credit: Mathieu Young, courtesy of FOX.

One of the biggest numbers on the finale for So You Think You Can Dance was a musical routine from A Chorus Line.  It would have been sensational without the surprise finish, which consisted of the judges decked out in top hats and tails.

The 3000-plus fans went bonkers the moment the judges stepped out from behind a handful of set decorations to begin their schtick.

And while Mary Murphy, Nigel Lythgoe and Mia Michaels were happy the secret ending was so well received, Michaels says it was more like strutting than dancing.  Still, they practice to keep it smooth and error free, but apparently even a good sashay is easy to flub.

Click onto video for all the info on the set up from Nigel Lythgoe, Mary Murphy and Mia Michaels.