Some boys of SMRookies share their 'Happiness' these days. What is the thing that make them happy?

In the 3rd episode of SM's RookieStation, Taeyong, Jaehyun, Jeno, Yuta and more seem like enjoying same song at the moment during their breaks. Which song it could be?

It's none other than their newly debuted fellow rookies 'Red Velvet's 'Happiness'. Who wouldn't feel livelier listening to this cheerful 'lalalalalalalalalala' song?

They are very supportive. Aren't they? Check out the clip below: