This are some videos of those surprises or spur of the moment or just improvising something for the sake of letting go.

This girl decided to take center stage and show how it's done.  It's cute to see the younger children getting into it too.

Need a bit of inspiration writing a new song or need some help with vocal accompaniment?  Grab a guitar and hit the subway!  Of course the original song "Next Stop" is the clear winner here.

Never seen a group of people deciding to do some Christman caroling?  Well, these folks took the idea and put it on steroids!  (Great singing)

Never let size be the judge of music enthusiasm

P.S.  I had to quick edit this post to add this one - dang, she dances like she's been doing it her whole life ;)

(Edit #2) Uh oh, I had a bit of Vodka and am having a bit "too" much (ain't too much unless it turns into a crash, but so far, so good)

I had to add this one also - they got in sync and ran with it.  Nice job (I even started singing harmony ... yeah, happens sometimes)

Robin: Holy Sheites Batman, edit #3?!

Batman:  It appears so, Robin.

Robin: So what do we do?

Batman: Don't worry, I've already called in a helicopter drop team in case an evacuation is necessary.  Just enjoy the ball game ... or dancing.  Up to you.

*Robin is transfixed by the dancing man* ;) LOL