Some animals sleep during the winter because the weather is very cold and it is difficult for them to find food. They sleep for a long time. This kind of winter sleep is called hibernation.

    If an animal moves a lot, it needs lots of food. Hibernating animals do not need to eat much because they don't move about. Their hearts beat(跳动) very slowly and they also breathe slowly. They always find a place out of danger. Their body fat can keep them warm.

    Some animals, like bears, may wake up from their hibernation in warm winter days and then quickly go back to sleep again when they see there is still snow outside. When the weather becomes warmer in spring, the animals start to wake up and look for food again.

    In 1986, Dan Harrison was on holiday in Kenya. He met a young elephant standing with one leg raised. Dan checked the elephant's foot carefully and found a large piece of wood in it. Dan got the wood out with his knife. The elephant's foot hurt and it turned around to look at the man. Dan stood quietly, thinking that the elephant may attack him. Finally, the elephant called loudly and walked away.

    Twenty years later, Dan was walking through the Chicago Zoo with his son. As they went near the elephant enclosure(围场), one of the creatures(动物) walked over to Dan and his son. The large elephant stared at Dan, lifted its front foot off the ground and then put it down. The elephant did that several times and called loudly.

    Remembering the thing in 1986, Dan thought this might be the same elephant. Dan climbed over the railing and walked up to the elephant. The elephant called again, wrapped its trunk around one of Dan's legs and threw him against the railing, killing him at once.

    Maybe it wasn't the same elephant.

    Let me tell you something about sharks. Sharks are among the oldest animals in the world. There are over three hundred and fifty different kinds of sharks in the world. Most sharks are about two metres long and live in the ocean. A shark can smell something in the water, for example, the blood of animals. That helps them find their food. Sharks mainly eat fish, other sharks and plants in the ocean.

    Most sharks bite(咬) people by mistake. They think a person is a large sea animal. When the sun goes down or comes up, sharks are looking for food. So at these times people shouldn't go swimming in the ocean.

    Today people kill sharks for food and their skin. The number of sharks in the world is dropping fast.