23um magnified into 200x

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.