Dog eyesight declines with age. Injuries and ailments can cloud their vision. Zero was a highly trained, driven alert dog. So, at competitions, when he started running into obstacles and falling off the ends of teeter-totters(跷跷板), his owner, San Francisco-area dog trainer Dianne Morey, was concerned.

As time passed, she noticed a pattern. The problems only occurred at competitions held in horse arenas, where yellow obstacles blended into the color of the sand covering the floor. Concerned about his eyesight, Morey took Zero to a vet, who diagnosed him with a genetic condition. Morey found the diagnosis “heartbreaking”. After one last competition—which he won—Zero retired. In the time since, he’s led a life full of activities like dock diving and hiking, where poor vision is less dangerous. While there’s no cure for his disease, protective eyewear has helped keep him safe while being active.

On average, dogs develop nearsightedness or farsightedness less often than humans, says Alexandra vander Woerdt at Animal Medical Center in New York City. However, their eyesight also declines with age. Injuries and some diseases such as glaucoma(青光眼) can cloud their vision. Thinking back, Morey realizes some behaviors—for instance, the way Zero poked his nose before entering a gate—were signs his vision was impaired.

Identifying vision issues in dogs isn’t as easy as with humans. Dogs don’t bark wrong letters on the eye chart, and they’re very good at adapting. Treatments for eye problems may include eyedrops, medications or surgery. Eyewear can also play a role in treating or preventing many issues. Many dogs don’t like eyewear at first. Zero was an exception, thanks to his training in agility and tricks, Morey says.

Scientists who study happiness know that being kind to others can improve well-being. Acts as simple as buying a cup of coffee for someone can boost a person’s mood, for example. Everyday life affords many opportunities for such actions, yet people do not always take advantage of them.

In studies published online in the Journal of Experimental Psychology, a behavioral scientist and I examined a possible explanation: people who perform random acts of kindness underestimate how much recipients value their behavior.

In one experiment, participants at an ice-skating rink in a public park gave away hot chocolate on a cold winter’s day. Although the people giving out the hot chocolate saw the act as relatively insignificant, it really mattered to the recipients. Our research also revealed one reason that people may underestimate their action’s impact. When we asked one set of participants to estimate how much someone would like getting a cupcake simply, for participating in a study, for example, their predictions were well calibrated (校准) with recipients’ reactions. But when people received cupcakes through a random act of kindness, the cupcake givers underestimated how positive their recipients would feel. Recipients of these unexpected actions tend to focus more on warmth than performers do.

Missing the importance of warmth may stand in the way of being kinder in daily life. People know that cupcakes given in kindness can make them feel surprisingly good. If people undervalue this effect, they might not bother to carry out these warm, prosocial behaviors (亲社会行为).

And kindness can be contagious (传染的). In another experiment, we had people play an economic game that allowed us to examine what are sometimes called “pay it forward” effects. In this game, participants allocated money between themselves and a person whom they would never meet. People who had just been on the receiving end of a kind act gave substantially more to an anonymous (无名的) person than those who had not. The person who performed the initial act did not recognize that their generosity would spill over in these downstream interactions.

These findings suggest that what might seem small when we are deciding whether or not to do something nice for someone else could matter a great deal to the person we do it for. Given that these warm gestures can enhance our own mood and brighten the day of another person, why not choose kindness when we can?

In general, just about every mammal (哺乳动物) relies on a community of gut bacteria (肠道细菌) for health and survival. Many animals have even developed to the point that closely related host species typically share more similar gut bacteria. But a new study has identified a converse phenomenon on one group of mammals — bats. The gut bacteria of closely related bats can be totally distinct from each other.

To learn about the relationships between bats and their gut bacteria, post-doctoral researcher Holly Lutz and her co-workers took samples of bacteria from the skin, tongues, and guts of 497 bats from 31 different species in Kenya and Uganda. They discovered bats have fewer bacterial species living in their guts than in their mouths and on their skin. What’s more, gut bacteria living in different bats are individually distinctive, following no apparent pattern. This struck the scientists as strange, since for most other mammals that have been studied, closely related hosts share more similar gut bacteria.

“There’s essentially no relationship between bats’ gut bacteria and their evolutionary (进化的) history,” says Lutz. While host identity is still an important factor in predicting the species of gut bacteria, this may simply be tied to where those bats live and what they eat. The fact that bats’ gut bacteria are more closely tied to where bats live than where those bats fall on the bat family tree indicates that developing a special relationship with just-right gut bacteria may not have been as important for bats as it has been for other mammals.

Lutz suspects that bats’ unique relationships with gut bacteria are related to the feature that sets them apart from other mammals: their ability to fly. “Bats have extremely shortened guts,” she explains. “Food takes just fifteen to thirty minutes to pass through a bat’s digestive system, a third as long as it would take for a similarly sized animal. That’s likely because a long, winding digestive canal would weigh the bats down.”