Wet skin and pain

When I was a kid there was a game we would play at school where the object was to break your opponents pencil with your own pencil. Afterwards the winner would get to smack the loser on the back of the wrist with two fingers. At some point it became known that before smacking the other person one should lick their fingers because the moisture would make it hurt more. Was there any truth to the idea that being hit by either a moist instrument or having wet skin makes a difference in pain sensitivity?