We've been to Japan a couple of months ago and happened to catch a performance of a Korean group, Snuper.
It is interesting that the audience takes part in the show, and is singling between the lines, as can be seen in this fan video, starting at 2:08 and 2:31:
Obviously, these lines do no appear on the regular version:
How does the audience know its part? And where do the lyrics come from - is it official, or fan-created?