The walrus has a specific respiratory and sensory physiology : it breathes through its nostrils but also through its mouth and its tactile vibrissae are its most developed sensory organs. Its horny 0.7 to 1.5in (2 to 4cm) thick skin is crisscrossed with folds and hollows and covered with short and rough hairs. Its color depends on its blood supply : it whitens on contact with the icy water which makes it ischemic and blushes in the sun because of the blood flow.