  Deterministic surfaces are constructs of which profile, topography and
textures are integral to the function of the system they enclose. They are
designed to yield a predetermined rubbing response. Developing such entities
relies on controlling the structure of the rubbing interface so that, not only
the surface is of optimized topography, but also is able to self-adjust its
behavior according to the evolution of sliding conditions. Inspirations for
such designs are frequently encountered in natural species. In particular, and
from a tribological point of view, Squamate Reptiles, offer diverse examples
where surface texturing, submicron and nano-scale features, achieves frictional
regulation. In this paper, we study the frictional response of shed skin
obtained from a Python regius snake. The study employed a specially designed
tribo-acoustic probe capable of measuring the coefficient of friction and
detecting the acoustical behavior of the skin in vivo. The results confirm the
anisotropy of the frictional response of snakes. It is found that the
coefficient of friction depends on the direction of sliding: the value in
forward motion is lower than that in the backward direction. Diagonal and side
winding motion induces a different value of the friction coefficient. We
discuss the origin of such a phenomenon in relation to surface texturing and
study the energy constraints, implied by anisotropic friction, on the motion of
the reptile and to establish a reference for comprehending the frictional
response we draw a comparison to the friction of human skin.
