Damn! I'll bet there is such a thing. I've heard stories.
But sorry, Dr. Dom, once the labia swells, it's a cunt. Especially when it's getting spanked!
context pensive, it was supposed to be flowery not surgical or clinical, I agree in part with what you are saying but the choice of labia was an attempt to point out the duality in the relationship, cunt in that context would seem to make it objectified, labia is a word that to me is more sensual.
The focus in bdsm from outside is generally on the violence and control as opposed to the sensuality shared. so this was an attempt at showing the care, along with the sting of the belt.