Weeding Dance Mount And Blade What Is The Dance The Crowd All Does At The End Of Weeds Season 5 Episode 1 "Wonderful, Wonderful"?

What is the dance the crowd all does at the end of Weeds Season 5 Episode 1 "Wonderful, Wonderful"? - weeding dance mount and blade

I am somewhat confused by the dance of notes that all the people in the mall at the end of the episode. Is this real? What is it? Nancy was asked if the guy next to the subject, he said something like "flashmop. Who knows what the deal is it?