Yesterday, the staff of The Master's Sun released this behind-the-scenes photo from the set of the show:

It appeared that So Ji Sub was in the middle of practicing his posture for filming the scene where he tries to avoid Tae Gong Sil (Gong Hyo Jin).

A representative from the broadcast mentioned, “Although So Ji Sub seems to be breathing fire, dominating the set with his hot enthusiastic performance, but as soon as he gets the OK sign, he transforms 180 degrees into his cute look.”