Dik-dik live in hot, dry scrub and rarely drink. Evaporative cooling by sweating or ordinary panting would cost water. The nasal passages of the snout are lined with a dense vascular bed, and when the animal is heat-stressed it moves air over this surface at high rate through the nose alone. Blood in the nasal mucosa cools as it passes, and the cooled blood returns toward the brain.
The arrangement forms part of a selective brain-cooling system found in several bovids, in which venous blood chilled in the nasal region cools arterial blood at the carotid rete before it reaches the brain. The effect is that body temperature can be allowed to rise while brain temperature is held down, saving water that would otherwise be spent on whole-body cooling.
The snout has a second use. Dik-dik have prominent preorbital glands just in front of the eyes, and the black secretion is pressed onto twigs to mark territory. The two functions are separate, and the marking glands are not part of the cooling apparatus.