Flash mob surprise

It's been fun to watch the evolution of flash mobs -- yes there is a name for them now -- these talented groups that appear to be so spontaneous.  

They sing and dance and delight people in the most unlikely places -- and then disappear.   Events such as "Doe a Deer" at the Antwerp train station, or the T-mobile dance at the Liverpool Street Station.  

Now, in keeping with the season, we have the "Hallelujah Chorus" in a mall food court!  (I'm guessing America for this one.)