f(x)'s Krystal got together with SNSD's Yoona and Seohyun backstage at Music Core to snap a cute shot of themselves. In the photo above, the girls are enthusiastically posing while doing the "cheek touch-up dance." The dance is part of the choreography in f(x)'s new song NU ABO. In the dance, the girls touch up their cheek as if they're putting on some makeup. Krystal uploaded the picture on to her me2DAY and surprised her fans. Sadly, sis Jessica isn't present in the photo. Krystal captioned, "I was happy to reunite with SNSD unnies at the broadcasting station." Netizens wrote, "So cute," "I want to touch-up their cheeks for them," and "They seem so close." They sure are cute!