When's the last time Christmas carolers came knocking on your door?  Caroling might be a holiday tradition that's gone by the wayside, but maybe it's about to make a comeback.

Improv Everywhere is a group in New York that plans huge flash-mob stunts, and their videos have been viewed over 370 million times on YouTube.

Their most popular one was a few years ago, when they had a bunch of people go to Grand Central Station and pretend to freeze in place all at once.

And for their newest stunt, four Christmas carolers went to a random family's house in New Jersey.  Then once they started singing, an entire CHOIR showed up to join in . . . followed by a 20-person orchestra that set up on the front lawn.