As the dolphin breathes the air leaves the blowhole at speeds of over 100mph. Complex nerve endings around the blowhole sense pressure changes so the dolphin knows exactly when the blowhole is in or nearing the air and can be opened. Water in a dolphin's blowhole will actually drown it so powerful muscles close the blowhole as it dives under the water again. The dolphin's eyes produce a special slippery secretion which protects the eyes from foreign objects and water friction. To sleep, a dolphin must shut down only half of its brain, as its breathing is under voluntary control.
Dolphins take short cat-naps, floating just below the surface, then slowly rising to breathe.
Often dolphins are very active during night time, for some this is their main feeding time. The dolphin's skin is completely smooth allowing the dolphin to move easily through the water, and also reduce heat loss. Their skin may bear rake marks from other dolphins teeth during play or mating, and can easily become badly sunburnt if they strand. Their bodies are very streamlined so they may swim at high speeds through the water, and an example of this is their ears. Dolphin's ears are barely noticeable marked only by a small hole just behind the eye.