It is a tall tale（夸张的故事）that terrifies most young children. Swallow a piece of chewing gum and it will remain in your body for seven years before it is digested. An even worse tale is that swallowed（吞） gum can wrap itself around your heart.

    But what does happen if you should accidentally eat a stick of gum? Chewing gum is made out of gum base, sweeteners, coloring and flavoring. The gum base is pretty indigestible(难消化的)—it is a mixture of different ingredients (成分) that our body can't absorb.

    Most of the time, your stomach really cannot break down the gum the way it would break down other foods. However, your digestive system has another way to deal with things you swallow. After all, we eat lots of things that we are unable to fully digest. They keep moving along until they make it all the way through the gut (肠子) and come out at the other end one or two days later.

    The saliva (唾液) in our mouths will make an attempt at digesting chewing gum as soon as we put it in our mouths. It might get through the shell（壳） but many of gum's base ingredients are indigestible. It's then down to our stomach muscles—which contract(收缩) and relax, much like the way an earthworm moves—to slowly force the things that we swallow through our systems.

    Swallowing a huge piece of gum or swallowing many small pieces of gum in a short time can cause a blockage within the digestive system, most often in children, who have a thinner digestive tube than adults—but this is extremely rare.

    A 525-year-old copy of a letter by Christopher Columbus, stolen from the Vatican, was returned this week. An investigation by the United States Department of Homeland Security and the Vatican located the letter.

    “We are returning it to its rightful owner, “said U.S. ambassador to the Vatican, Callista Gingrich, at a ceremony in the Vatican Library. Columbus wrote the letter to the king and queen of Spain after discovering “The New World.” He described what he had found and requested money for another trip. His original letter was written in Spanish. But several copies of a Latin translation were made to spread news of his discovery to the royal courts of Europe and the Pope.

    One of the Latin letters, copied by Stephan Plannack in 1493, was put in the Vatican Library. Known as the Columbus Letter, it has eight pages, each about 18.5 cm by 12 cm. In 2011, an American expert in rare manuscripts received a similar looking letter. After reviewing it, he decided that it was real. The year before, the same expert had studied a Columbus Letter in the Vatican Library and suspected that it was a fake. One reason was that the stitching (针脚) marks on the letter were not the same as those on the cover. The letter in the United States, however, had the exact same stitching marks as the leather cover of the fake letter he had studied in the Vatican.

    The expert, who was not identified, contacted Homeland Security art investigators, who began working with Vatican inspectors and rare book experts. They believed that someone took the real letter out of its cover at the Vatican Library and replaced it with an artificial one. Archbishop Jean-Louis Brugues is the Vatican's chief librarian. He said, “We do not know exactly when the substitution took place. We will probably never know who the forger (伪造者) was.”

    Their investigations found that Marino Massimo De Caro, a well-known Italian book thief, had sold the real letter to a New York book dealer. De Caro is serving a seven-year prison sentence in Italy for stealing about 4,000 ancient books and manuscripts from Italian libraries and private collections. The late collector David Parsons bought the letter for $875,000 in 2004. After the investigations, his widow agreed to return the letter to the Vatican Library. Officials said the letter is now worth about $1.2 million.

    Frequently, we speak about people being “color-blind” but very few of us are. Even those who describe themselves as color-blind are normally just color lack. A strongly, color-blind person will still be able to tell 20 different colors, compared to the 100 or so that normal-sighted people see.

    Pingelap, a tiny island in the Pacific, is a beautiful spot but one that has a genetic trouble. It is known as Color-blind Island because so many people who live on this remote island can only see black and white.

    Not being able to see colors is bad enough. But one islander, Herrol, who's a fisherman, also struggles in full sunlight because all he sees is a painful burnt-out image. “I find it difficult to go outside in the sun,” he says, “because when it's sunny I cannot see to do my work.”

    But if being truly color-blind is rare, why is it that around 10% of the population of Pingelap live in a totally black and white world?

    Well, we know that in 1780 the population of Pingelap was all but wiped out by a tsunami (海啸). As few as 20 people survived, one of whom was the king. It's believed he had a genetic fault that causes colour-blindness and he passed this fault on to his many generations.

    There is one advantage. Herrol can see well, really well, in the dark. So when it gets dark, Herrol and his friends get in their boats and hunt flying fish. They hang up flaming torches and the fish are attracted to the flames. “This type of fishing is fun,” Herrol says, “especially if we catch plenty. So even though it's hard work we enjoy it.”

    Exercise could not only benefit your body, but also imp rove your memory, researchers found recently. In their paper published on Monday, researchers from the University of California, Irvine in the United States and the University of Tsukuba in Japan introduced their experiment and conclusion.

    Scientists invited 36 volunteers who were in their early 20s to do 10 minutes of light exercise before taking a memory test in which they were shown pictures like broccoli(西兰花)or picnic baskets and asked to recall them later. The same experiment was repeated with the same group of volunteers without exercising. "The memory task was really quite challenging ,said Michael Yassa, co-author of the study and a neuroscientist (神经科学家)at the University of California, Irvine. "We used very tricky similar items to see if they would remember whether it was this exact picnic basket versus (对抗)that picnic basket. "

    Researchers also scanned brains of some of the participants during the experiment. They found strengthened communication between regions involved in the storage and recollection of memories in brains of those who had exercised. This suggested that just 10 minutes of light exercise like walking, yoga or Tai Chi might increase memory power.

    As all the volunteers in the experiment were relatively young, researchers are still working to look at the effects of light exercise on older people. " Our future goal is to try to develop an exercise prescription (处方)that can be used by older adults who might have disabilities or mobility impairments, but can still adopt very simple exercise rules of life and be able to, perhaps, delay cognitive decline temporarily," said Yassa.

Learning a second language

    Some people learn a second language easily. Other people have trouble learning a new language. How can you help yourself learn a new language, such as English? There are several ways to make learning English a little easier and more interesting.

    The first step is to feel confident about learning English. If you believe that you can learn, you will learn. Be patient. You don't have to understand everything all at once. It is natural to make mistakes when you learn something new. We can learn from our mistakes.

    The second step is to practise your English. For example, write in a diary every day. You will get used to writing in English, and you will feel comfortable expressing your ideas in English. After several weeks, you will see that your writing is improving. Besides, you must speak English every day. You can practise with your classmates after class. You will all make mistakes, but gradually you will become comfortable communicating in English.

    The third step is to keep a record of your language learning. You can write this in your diary. After each class, think about what you did. Did you answer a question correctly? Did you understand anything the teacher explained? Perhaps the lesson was difficult, but you tried to understand it. Write these achievements (成就) in your diary.

    You must be active in learning English and believe that you can do it. It is important to practise every day and make a record of your achievements. You will enjoy learning English, and you will have more confidence in yourself.

Living a healthy lifestyle lies in forming the right eating habits. Here are some of the good habits you can develop when it comes to healthy eating.

Drink plenty of water, you must drink at least 8 glasses of water a day. You may need even more water if you are in a hot environment or if you are exercising.

Eat breakfast. Breakfast is the most important meal of the day. A recent study has shown that those who eat breakfast will use an average of 100 calories less during the day than their colleagues who skip breakfast. They will also be able to concentrate better.

Don't skip lunch. If you do so, your blood sugar level will drop and your metabolism (新陈代谢) will slow down. When you get home you are starving and eat everything you can find.

We all need to snack from time to time, but please choose your snacks carefully. In fact, it's a good idea to eat two healthy snacks besides your three main meals. Choose healthy snacks like fruits, low fat yogurt, cottage cheese with apple sauce.

Eat your fruits and vegetables. We should eat at least 5 servings of fruits and vegetables a day. Take a piece of fruit for a snack, add some bananas and raisins to your favourite breakfast cereal (谷类食物), have a salad of lunch, and eat at least one vegetable at dinner each night.

Do not eat your dinner too late. Try to eat dinner at least 3 hours before you go to bed, this will give your body a chance to digest most of the food before you rest for the next 8 hours. Plan dinner for the week ahead of time and make sure you have everything you need in the house so other family members can get ahead start on dinner if you have a late meeting at the office.