Ochiai suggests that the (standing, in some variants kneeling) person mourns the death of the person the bones belonged to. Henshall suggests that the later variant (with a fallen person) reinforced the idea of death already expressed by bones 歹 (I’m guessing he means that the person fell down and died). Or, encompassing both variants, simply, a person who turns into a skeleton is dead (Japanese Wikipedia defines the expressed meaning as ‘a person dies and turns into bones’).
1. and are impressions of oracle bone character shapes by Ochiai (p. 72).
