Only humans speak using words. But all kinds in the animal world can communicate in one way or another. Maybe you have heard about the way bees dance around to send messages to each other and the way dogs bark in different ways to give warnings, to be friendly or to be playful. But did you know about infrasonic communication used by elephants? This is how it works:

    Humans hear low sounds like thunder rumbling in the sky. But we don't hear sounds lower than this. However, animals such as elephants and hippos can hear much lower sounds than humans can. And what's more, they can make those low sounds as well, and they use them to communicate with each other. This is known as infrasound.

    The amazing thing about infrasound is that it travels over several kilometers. Higher-level sounds like the one people can hear, don't travel well through walls, leaves, trees and so on, which is why we can't hear sounds from more than 100 meters away. But infrasound is much stronger and things like grass and trees have no influence on it. Therefore, it can travel much further. Elephants can hear infrasonic calls from four kilometers away!

    There have been reports of people watching groups of elephants feeding or resting and then the elephants suddenly all stopped what they were doing for no reason at all. They obviously heard a warning call from a long way away, but the people didn't hear a sound. In places like a zoo or wildlife park where you can get nearer to animals, it is a bit easier to sense when infrasonic sounds are made. When you stand near mother elephants with their babies in a zoo, you may notice a slight rumbling in the air every few minutes—not loud or strong, but clearly noticed. This is infrasonic communication—the mother elephants “talking” to their babies.

    You may know about "junk food" like French fries. But do you know about "junk sleep"?

    Recently, a British survey found that electronic products（电子产品）in teenagers' bedrooms are affecting（影响）their sleep. The survey was done among 1,000 British kids from 12 to 16. It found that 30 percent of them got just 4 to 7 hours of sleep every day. But doctors say they need 8 to 9 hours.

    Almost a quarter of the kids said they fell asleep more than once a week while watching TV, listening to music or using other electronic products.

    "This is very worrying." said Dr. Chris Idzikowski, "We call it "junk sleep". It means you don't get enough sleep and the quality（质量）of the sleep is bad, too. If you don't get good rest, you won't perform well in school the next day."

    The survey found that 40 percent of the kids felt tired each day, with girls between 13 and 16 feeling the worst. Nearly all the teenagers have a phone, Mp5 or TV in their bedrooms. And many of them have all three.

    If your pen broke at school today, what would you do? You would go to a shop and buy a new one. What if you could simply print out a real, working pen with your 3-D printer without leaving your room?

    Ten years ago people could only see 3-D printing in science fiction movies. But now 3-D printing is here and it's bringing big changes.

    Unlike normal printing that can only copy a 2-D picture with ink. 3-D printing can build almost anything made from material. The printer layers(分层) the material in different shapes to create the object you want to be copied.

    The 3-D printer has been used to make many different things. People have made cups, cars and even an airplane with it. Doctors have been using 3-D printers for several years. People's nervous systems(系统) have been printed out in 3-D form in medical research. Some body parts have been printed and used in hospital. Several months ago, doctors used a 3-D printer to rebuild the face of a person who had a bad accident. In the future, it is expected that the printer will make human organs(器官)to save more lives.

    However there are drawbacks to the printer. At the moment, printing can be quite slow and it's still rather expensive. The average(平均的) price of a household printer is around $1,700, not including the cost of the materials.

    But as the technology develops, it shouldn't be long before disadvantages are improved. Only time will tell where this new technology will take us.

    How do you light up the night sky? The answer is by using electricity. But did you know that nature can glow (发光), too?

    Scientists have found many glowing living things. Most of them live in the ocean. Some use their lights to talk to each other. Others use them to hunt, to mate (交配) or to protect themselves. The vampire squid (幽灵蛸), for example, uses a cloud of light to scare enemies.

    Scientists around the world are looking at this kind of light for new ideas. In 2013, the US company Gleaux said it has created the world's first light-producing plant, the Daily Mail reported. It is a genetically-modified (转基因的) plant. It can glow like a firefly.

    Alexander Krichevsky, the company's founder (创始人), and other scientists hope that in the future, glowing plants could replace lamps and glowing trees could light up highways. Krichevsky also hopes the technology could be used in farming. Farmers could know when their crops need water or are ready to be picked if they glow.

    While Gleaux is working on glowing plants, the French company Glowee is trying to use glowing bacteria (细菌) to light up shop windows and street signs. It's the same type of bacteria that cause a type of squid to light up, New Scientist Online reported.

    "Our goal is to change the way we produce and use light," said Glowee founder Sandra Rey. "We want to help reduce the 19 percent of electricity consumption (消耗量) that is used to produce light.

    Gardening is popular in many parts of the world. It brings us sweet smelling flowers, fresh fruit and vegetables. But you can get more from your garden.

    Gardening helps to keep healthy. Today's people sit indoors for too long and don't get much exercise. When you garden, you have to move around. It's a good chance for you to exercise your body by watering flowers or doing some digging. Besides, when you are in your garden, you can feel the warm sunshine. This means you are getting Vitamin D. It helps your bodies use calcium (钙), which is necessary to keep your bones (骨骼) strong.

    It gets them off computers, televisions and phones. Gardening can be a great teacher to teach children about nature and healthy eating. It can also help them to understand the meaning of "No pains, no gains."

Gardening is a great way to meet people and build relationships. When you are gardening, you are outdoors. So it is a perfect time to communicate with your neighbors. Most people love to talk about their hobbies, and so do gardeners. They usually enjoy showing people what they are growing. And most enjoy sharing advice and stories about their gardens.