There are different kinds of animals living on the earth. Some of them are small, and some are big. But they all sleep! All animals need sleep. Some sleep a little, others sleep a lot, and some get their zzzz's in interesting ways.
Light Sleepers
Giraffes sleep for just a few hours each day. It is dangerous for them to sleep for a long time. Why? First of all, predators, like a lion, might get them at that time. Also, it usually takes giraffes about one minute to stand up and run away at once, so they have to stand up when they sleep. However, they often need to lie (躺）down to have a deep sleep for half an hour.
Big Sleepers
Koalas live in Australia. They may sleep 18 to 20 hours a day! They wake up, eat leaves and then go right hack to sleep. Lions are predators. They get other animals as food. Lions are big sleepers, too. When lions are not eating, they usually play and sleep. They can sleep well. After all, who wants to wake up a sleeping lion?
Half-Asleep Sleepers
Scientists found that dolphins can make half of their brain(大脑）sleep at a time. The other half stays awake! Like dolphins, when some birds fly far across the sea, they can also sleep with half of their brains and the other half keeps flying. Other birds sleep for a short time when they float (漂浮） on air over the sea. They fly and sleep, fly and sleep. After they get home, they sleep a lot.
