画龙画虎难画骨huà lóng huà hǔ nán huà gǔ

in drawing a dragon or a tiger,you show its skin,but not its bones—it is difficult to know a man’s heart
❍ 杨雄听了，心中火起，便骂道：“～，知人知面不知心。……”(《水浒全传》576) Yang Xiong was very angry at this,and said，“In drawing a tiger,you show its skin,but not its bones: in knowing a man,you may know his face,but not his heart.”