Dolphins

Dolphins are very smart and playful. They breathe air like us and communicate with whistles and clicking sounds. They often swim in groups and leap out of the water.

For scientists

Dolphins "see" with sound: they emit clicks and read the echo for the shape, size and distance of their prey (echolocation). Each dolphin has its own signature whistle, almost a name, that the group uses to call it. When sleeping, only one half of the brain rests at a time, so the animal can keep surfacing to breathe.

Source: NOAA

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