In 2015, astronaut Scott Kelly made himself a guinea pig for NASA's "twins study," designed to see what spaceflight does to the human body. It was for all the people who dream of human journeys to Mars and other destinations in space. Kelly rode a rocket into space and spent nearly a year on the International Space Station in low Earth orbit, while his identical twin brother, Mark Kelly, served as the comparison subject and stayed on Earth's surface.

The full results, published Thursday in the journal Science, showed that Scott Kelly experienced numerous physiological and chromosomal（染色体的）changes during his long stay in orbit, including changes in gene expression. His immune system went on high alert, both when he went to space and upon returning to Earth. His body acted as if it were under attack.

One of the most dramatic findings concerned epigenetics（实验胚胎学） — how genes are turned on or off to produce proteins. Gene expression changed in both Kellys during the study but in significantly different ways. The study found that more than 90 percent of Scott Kelly's gene expression changes returned to normal when he landed on the surface. His telomeres（染色体端粒）, structures which break over time as part of the natural aging process, lengthened in space. But that didn't necessarily mean being younger, the study found, because most telomeres shortened dramatically when he returned to Earth.

Months later, tests showed that slight changes in telomeres length still remained and left some influence on Scott Kelly, which means he and his brother are no longer identical twins. "He might be at some increased risk for cardiovascular disease or some types of cancer," said Susan Bailey, a biologist at Colorado State University who led one of the investigations in the study.

However, the researchers, echoing what NASA has suggested previously, said the twins study turned up no showstoppers — no shocking health consequences that would surely prevent a human mission to Mars or similar long-duration mission.

Scientists have already studied how dogs respond to people’s behavior and speech. But researchers are just scratching the surface of human-cat interactions. House cats do appear to respond to the expressions on people’s faces. Cats can also tell different human voices. But can cats recognize their own names?

Saito, a psychologist at Sophia University in Tokyo, and her colleagues decided to find the answer. They asked the owners of 77 cats to say four nouns of similar length followed by the cat’s name. Cats gradually lost interest in each random(随机的) noun. But when the owner said a cat’s name, the cats reacted strongly. They moved their ears, head or tail, changed their back paw’s position. And, of course, they miaowed.

These findings mean that cats join the ranks of animals that have shown some sort of response in experiments to the names people give them. Those animals include dogs, dolphins, apes and parrots. It’s hard to compare the number of words across species, though. Some dogs, for example, can tell the difference between hundreds of human words.

The study makes a strong case that cats are perfectly capable of recognizing their own names. Getting a treat or hug as a reward is part of how cats learn to recognize a name. However, owners may also use their cat’s name in a negative setting, like yelling at Fluffy to get off the stove. As a result, cats can probably learn to associate these familiar utterances with good and bad experiences, Saito notes. And that might not be great for human-cat relations. So only using a cat’s name in a positive context and using a different term in a negative context could help cats and humans communicate more clearly.

So cats may recognize their names. But will they come when called? Don’t get your hopes up.