We all cry for water when we are thirsty. But do you know, in very hot, dry weather, plants also make very low sounds as if they are crying for help?

    You see, in a plant's stem there are several hundred "water pipes" that bring water from soil all the way up to the leaves. When the ground turns dry, it becomes harder and harder for plants to do this.

    On very hot days, plants have to get any water that they can get.

    Scientist Robot Winter has found out that when plants can get no water, their "water pipes" snap(发出声音). When that happens, the whole plant vibrates(振动) a little.

    Robot knows that healthy, well-watered plants are quiet.  He also knows that dry plants are many insects' "favourite" and they often attack(袭击) them. How do the insects know which are healthy plants and which are not? Robot thinks that the insects may hear the plants "crying" and they may come to kill them.

    One day, you open the fridge and find some moldy (发霉的)food. But before you can throw it away, your mother stops you. She doesn't want to waste food. She cuts off the moldy part and eats the rest. Is it safe to do this?

    Mold (霉菌)can grow on almost all kinds of food. Mold is usually green, white, black or grey. Mold makes food soft and changes its color. Moldy food tastes quite bad一一and it's not safe to eat.

    If you find mold in soft food, just throw it away. Soft food, such as bread, tomatoes or hot dogs, usually contains water. This allows mold to easily grow below its surface. Bacteria (细菌)can also grow along with it.

    But it's easy to remove mold from hard food. The mold can't grow very deeply inside this kind of food. According to the BBC, you should cut about 2.5 cm around and below the mold to remove it. It's OK to cut the moldy parts out of hard food and eat the rest. But if the food is completely covered with mold, you should still throw it away.

    Most kinds of mold are bad for us. But some kinds of mold can be used to make food. For example, penicillium (青霉菌)can be used to make many types of cheeses, such as blue cheese. These cheeses are safe to eat--and they're quite delicious as well.

    For us humans, one of the greatest experiences is to taste all kinds of delicious food. But for penguins, they cannot get a taste of this happiness. That's because penguins can't actually taste the delicious flavors (味道) of their favorite food-fish!

    Scientists from the University of Michigan examined the genome (基因组)of five species of penguins. They found that no one can taste umami (鲜味),the flavor of meat or fish, the BBC reported.

    Many animals have five basic tastes: sweet, sour, salty, bitter and umami. But according to genetic data, penguins are believed to have only sour and salty tastes.

    These findings are surprising and puzzling. And scientists don't have a good explanation for them. But they have a few ideas.

    First, one of the umami genes doesn't work in cold temperatures. "It's about zero degrees when they eat cold fish," Zhang Jianzhi, the lead scientist, told the Daily Mail, so even if the penguins had a functional (功能的)gene, it might not work when they needed it.

    Second, penguins' tongues (舌头) are very special which may have something to do with their lack of taste. Instead of being covered with taste buds which help to taste food, penguins' tongues are very spiky. This is better for them to hold slippery (滑的) fish than tasting them. One study even showed that some types of penguins don't even have taste buds.

    However, penguins seem to be managing just fine.

    "Their behavior of swallowing food whole, and their tongue structure and function, suggest that penguins need no taste perception," said Zhang.

    Big data (数据) is a lot of sets of information that are put together so they can be used by a computer program. The computer program looks for different kinds of answers or patterns in the data. Big data can have different kinds of information from many sources, such as information that comes from schools, social media sites, companies, and governments. One set of data can have people's names and addresses. Another set can have what they like, where they go to school, and how much time they spend on the computer.

    Big data can be used in many ways. The government uses it to understand how many people travel on buses or trains. This information is then used to make bus or train systems better. Some schools use big data to understand which children may need extra help in class. The teacher can then give certain students more help or support so those students can succeed in school. Companies use big data, too. It helps them understand who buys their products. For example, one company uses weather data to see when people eat the most ice cream.

    Big data can be used for good reasons. Some hospitals use big data to predict if a baby who is born too early will get sick. The hospital can then take extra steps to take care of that baby so he or she does not get sick. Big data can also be used for bad reasons. It can be used to predict which kinds of people are likely to break the law or hurt others, even if they have not done anything wrong.

    How can big data be used for good and bad things? It is because the computer programs used to look at big data and understand it are written by people. People think a certain way. Because they think a certain way, they build a model of those ideas. These ideas are then used to look at the data. Sometimes, these ideas are helpful for people or businesses. Other times, bad ideas can cause problems for certain groups of people.

    The years from A.D 500 to 1450 are called the Middle ages. Sometimes they are also called the Dark Ages since few people had an education during that time. Still, there were lots of new ideas and inventions. Many of them came from China.