A metric lick is expressed in moles of substance removed from the surface per square centimeters of tongue surface in contact with the surface. Associated with any measurement made in licks is a saliva index, which indicates how many moles of saliva were transferred, on average, to the surface.

Figures on how many metric licks are in one swipe of the tongue on different surfaces are appreciated. I may generate them myself when I have a chance (it's midnight, and I don't want to go around licking things right now) - s_alanet