Now XUN PIN has been related as Dark Female Mysterious Female but also as Dark Valley or Deep Valley.
Note the characters used
Xuan dark hidden A sealed Cocoon from which life may emerge
Pin usually translated as Female Animal but some dictionaries online an dprint note that it also means valley. I think either the early scribes used the same character to write a word that sounded the same maybe in two dialects but had a different meaning or the word has changed meaning and I suspect the original meaning was either valley or cleft or er deep opening.
I couldnt find a image of bi in small seal script so drew one in Inkscape and added two even more archaic forms to the image. Note that Bi the right element in the character has changed its orientation over the centuries.
Also appear in mind the left hand element "cow" actually refers to bovines and other grazers and browsing herd animals hence female. Though I'm thinking possibly a euphemism for an opening female mammals have which would explain the er reluctance of male scholars to discuss why a minority uses valley and the link to valley spirit of dark female or hidden valley or deep vale or ...
er hum er ... yeah ... maybe ... what do you think?