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. They're also the ones who started the "no pants" subway rides in New York, and people in more than 60 cities around the world did it last year. 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.