Many canines will lick for a multitude of reasons: obsessive/compulsion disorder, anxiety, boredom, investigatory behavior, positive feed-back (via pleasurable stimulation of the vomer organ), greeting behavior and establishment of social pecking order.
I don't have an answer for your particular situation because I don't have enough detail of your home/pet situation. I would consult with a veterinarian who has a strong animal behavior background to determine the "why" of this licking demonstration.
Suffice to say this should not be a problem by itself, only if dangerous substances exist in the home environment that may cause trouble if ingested.
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124