- They Sleep with One Eye Open (Unihemispheric Sleep): Because dolphins are mammals, they breathe with lungs and take every breath consciously. To avoid drowning and stay alert to potential predator threats, they put only one half of their brain to sleep. During this time, the other half remains awake, and they continue swimming with the eye on the opposite side open. - They Give Each Other Names: Each dolphin has a unique, high-frequency "whistle" sound. Scientists have discovered that these whistles function just like human names. When calling out to another dolphin, they can imitate that individual's unique whistle. - They Are Among the Rare Animals That Use Tools: Particularly in Australia, certain bottlenose dolphins cover their snouts (rostrums) with sea sponges while searching for fish among sharp rocks and sea urchins on the seafloor. They also teach this technique to their calves, passing it down from generation to generation.