[infinite monkey]

I was like wtf is skin friction. Well I'll be a monkey's aunt...found this article:

The skin over most of the body is relatively smooth. 'Friction Ridges', however, are found on the digits, palms and soles. They are called 'friction' ridges because of their biological function to assist in our ability to grasp and hold onto objects. They have been compared to fine lines found in corduroy, however unlike corduroy, ridges vary in length and width, branch off, end suddenly and, for the most part, flow in concert with each other to form distinct patterns. The ridge path can sometimes be quite fragmented...so much so as to show what appears to be individual ridge "units" present on the volar surface. There are approximately 2,700 ridge "units" per square inch of friction skin. Each ridge "unit" corresponds to one primary epidermal ridge (glandular fold) formed directly beneath each pore opening.

http://ridgesandfurrows.homestead.co...tion_skin.html