And the priest shall look on the plague in the skin of the flesh: and when the hair in the plague is turned white, and the plague in sight be deeper than the skin of his flesh, it is a plague of leprosy: and the priest shall look on him, and pronounce him unclean.
The priest examines the skin's plague, checking if the hair turns white and the plague goes deeper than the skin. If so, it's leprosy, and he declares the person unclean.