Would you be able to sleep with one eye open? Bottlenose dolphins (宽吻海豚) can. When they sleep, only half of their brain goes to sleep. They sleep with one eye open to stay safe. Half of their brain sleeps for about two hours before the other half of their brain gets a chance to sleep. Sometimes, the dolphins will keep swimming while they are sleeping.

Dolphins are not fish—they are mammals (哺乳动物). These mammals have lungs (肺). And they don’t have gills (腮) like fish. They are also warm-blooded and have to go to the surface of the water to get air into their lungs. Dolphins don’t lay eggs. Their young are born alive and they drink milk from their mothers. Dolphins are one of the smartest animals in the world. There are many stories about how they save people out of water. They are able to solve many problems like humans. They can even use tools to catch fish. But their cleverness doesn’t end there.

Dolphins can also pass on anything they learn to other dolphins, like interesting fishing skills. They communicate with each other in many ways. They use different sounds to talk to each other. Dolphins know the “voices” of other dolphins and even know exactly who is making which sound. Another thing that shows their cleverness is that they can also know themselves in a mirror (镜子) and check different parts of their body in it.