At the press conference on December 8, Lee Kwang Soo said, "Song Joong Ki immediately accepted my request for a cameo even before seeing the script. I'm very thankful for such friend." He continued, "I actually didn't know that many female staff members existed until that scene [with Song Joong Ki]. There were also some who I've never seen before."
Director Ha Byung Hoon agreed and said, "I didn't realize that we had that many staff members until Song Joong Ki came to the set. There were about 2 times more people than usual, and they were staring to the point that it was scary."
He also added, "Song Joong Ki worked very hard, and he prepared a lot. He also took pictures with all the staff members before leaving. I regret not taking one with him."
The sitcom version of 'Sound of Heart' will broadcast on KBS starting December 9.