4 . Scientists have studied cats’ social relationships—both with other cats and humans—but it can be difficult to tell whether two cats are playing or fighting, says cat behavior researcher Noema Gajdoš-Kmecová.

To assess and classify interactions, Gajdoš-Kmecová and colleagues watched about 100 videos of different cats interacting in pairs. After viewing about one-third of the videos, Gajdoš-Kmecová identified six types of behaviors, including wrestling and staying still. She then watched all of the videos and noted how often each cat displayed one of the specific behaviors, and for how long. By running statistical analyses on the behaviors, she found three types of interactions between the cat pairs: playful, aggressive and intermediate. To confirm the outcome, other members of the team also watched the videos and classified each interaction between cats.

Some clear connections appeared. Quietly wrestling, for example, suggested playtime, while chasing and vocalizations(发声), like growling, hissing or gurgling, implied aggressive encounters.

Intermediate interactions had elements of both playful and aggressive encounters, but especially included prolonged activity of one cat toward the other, such as pouncing(突袭) on or grooming(梳毛) its fellow cat. These in-between encounters could suggest that one cat wants to keep playing while the other doesn’t, with the more playful cat gently pushing to see if its partner wants to continue, the authors say.

This work provides an understanding of cat interactions for the first time, Gajdoš-Kmecová says, but it’s just the start. In the future, she plans to study more subtle behaviors, like ear twitches and tail swishes. Gajdoš-Kmecová also stresses that one potentially controversial encounter doesn't necessarily signal a terrible cat relationship.

5 . In a study, published in the journal Proceedings of the Royal Society B: Biological Sciences, a team of French researchers at the University of Sorbonne Paris North demonstrated that ants have the potential to act as early stage cancer detectors.

“We knew that ants can be easily trained,” Baptiste Piqueret, who led the study, said. “Furthermore, they have an efficient sense of smell. We then combined these two abilities and tested whether ants were able to detect the smell of cancer or not.”

Tumor (肿瘤) cells produce specific chemical compounds that allow them to be distinguished from healthy tissues. These are known as cancer biomarkers. Animals can be trained to sniff out (嗅出) these chemicals and thus identify when a patient has cancer.

In the present study, worker ants of the species Formica fusca — commonly known as the silky ant —were trained to recognize cancer biomarkers of an extremely aggressive human breast cancer. The urine (尿液）of mice carrying these tumors was collected and presented to the trained ants, alongside urine from tumor — free mice.

After just three rounds of training, where the ants learned to associate the smell of cancer biomarkers with a sugary treat, they spent approximately 20 percent more time near the urine from the tumor - bearing mice than the urine from those who were tumor-free.

In the past, dogs and mice have also been shown to sniff out cancers. But ants would provide a particularly attractive alternative as they are relatively easy to keep, they don't require expensive rearing (饲养) facilities, and it appears that they can be trained to recognize specific odors in relatively few trials.

7 . Dogs and humans clearly have a special bond. But do dogs, like humans, produce more tears at times when they are flooded with emotion? A new study, which may be the first to look at this question, says that, indeed, the eyes of dogs do well up with tears. In fact, it happens regularly when they’re reunited (团聚) with the owners.

“We found that dogs produce tears associated with positive emotions,” says Takefumi Kikusui of Azabu University in Japan. “We also made the discovery of a chemical, oxytocin, as a possible mechanism (机制) behind it.”

Kikusui and his colleagues made the discovery after one of his two dogs had babies 6 years ago. He noticed that, when his dog was nursing the babies, something changed in the dog’s face — there were tears. Those tears don’t fall as they often do in humans but they do get teary eyes. “That gave me the idea that oxytocin is likely to increase tears,” Kikusui says.

They decided to run a reunification experiment and see if oxytocin brought dogs to tears. First, they used a standard test to measure dogs’ tear volume (量) before and after reuniting with their owners. They found that tear volume indeed ascended when they got back together with the familiar human and not with a person they didn’t know. When they added oxytocin to the dogs’ eyes, their tear volume also increased. That finding supports the idea that the release of oxytocin plays a role in tear production when dogs and their owners get back together. They also asked people to rate pictures of dogs’ faces with and without artificial tears in them, and it turned out that people gave more positive responses when they saw dogs with teary eyes. These findings suggest that dogs’ tear production helps to develop stronger connections between people and their dogs.

Kikusui says they had never heard of the discovery that animals produce tears in joyful situations, such as reuniting with their owners, and that they were all excited that this would be a world first!

10 . My childhood is closely associated with the Yellow River. My father ______ to take me with him on his trips to Longyangxia Reservoir. At Longyangxia, I was ______ by the beauty of nature and as a child, I wanted to stay there and ______ up with the Yellow River. Li Bai, a poet of the Tang Dynasty, praised the ______ water of the Yellow River. He saw it as coming down from heaven and ______ the people living on the banks of the river. However, in 1997, for about 330 days, not a single ______ of water from the Yellow River went into the sea. ______ are not the only punishments given by nature. A friend of my father, a university professor, is doing ______ on the Yellow River. According to him, since there is no longer enough water to ______ the mud, the river may soon change its course ______ we allow this situation to continue. This is the ______ of unbalanced growth. If we’d taken care of the vegetation in the upper and middle ______ of the river, we would still be able to ______ it as Li Bai described it.

In fact, people have begun to ______ the problem. I have seen farmers _______ trees on mountain slopes in Shanxi province. I have seen them ______ up the hillsides carrying heavy buckets of water collected several kilometers away down in the valley to ______ around the trees. These farmers are ______ helping our Yellow River, just as the river has helped them. These unsung heroes gave me the confidence that with hard work of us all, we and nature will grow together, and ______ in the future, we will be able to drink the ______ water from the Yellow River-our mother river.