Research has shown that some species of monkeys, birds and domesticated animals can even distinguish among different faces by looking at photographs alone. Scientists have also wondered whether domesticated animals that have coexisted with people for thousands of years can recognize different human faces.

Léa Lansade of the French National Research Institute did an experiment to find out how well horses can recognize individual people in photographs. She and her team first taught the horse show to “choose” between two side-by-side images by touching their noses to a computer screen. The horses were then shown photos of their current keeper alongside faces of unfamiliar humans. They had never seen photos of any of the people before. The horses correctly identified their current keeper and ignored the strangers face about 75 percent of the time, significantly better than chance. What’s more, the horses also preferentially picked photos of their previous keeper—a person they hadn’t seen in six months. In fact, even though the horses didn’t get it right every single time, they were at least as accurate in picking out their previous keeper as they were at identifying their current one.

The results suggest that not only can horses tell the differences between familiar and unfamiliar human faces, they can also understand that photographs are representations of real life. In addition, horses seem to have a long-term memory for human faces.

In future experiments, the researchers would like to test whether looking at photos of people that they have had bad experiences within the past might cause horses to act anxious or even avoidant. So maybe think twice before doing anything that might give a horse a long face.

New research led by the University of Colorado Boulder has found the engineering secrets behind what makes fish fins (鱼鳍) so strong yet flexible. The team’s findings could one day lead to new designs for airplane wings that change their shape with the push of a button.

Francois Barthelat, senior author of the study, noted that fins can “do wonders” even though they don’t contain a single muscle. “A fin is made of many ways,” said Barthelat. “Each of those rays can be controlled individually just like your fingers, but there are 20 or 30 rays in each fin.”

Barthelat and his colleagues used a range of approaches, including computer simulations and 3D-printed materials, to dive deep into the secrets of the structures. They reported that the key to fish fins may lie in their unique design. Each ray in a fin is made up of multiple segments (段) of a hard material that lie on top of much softer collagen (胶原), making rays the perfect balance between flexibility and strength.

He and his team decided to use computer simulations to examine the mechanical functions of fins. They discovered that those segments can make all the difference.

“Pretend for a moment,” Barthelat explained, “that fish fins are entirely made up of collagen. They could bend easily, but wouldn’t give fish much pulling force in the water. Rays made up of solid materials would have the opposite problem — they’d be too hard.”

The researchers further tested the theory by using a 3D printer to produce model fish fins made from plastic, some with hinges (铰链) built in and some without. The team found that the segmented design provided better combinations of strength and flexibility.

“We like to pick up where the biologists and zoologists have left off, using our background in the mechanics of materials to further our understanding of the amazing characteristics of the natural world,” Barthelat said.

Most people feel that dreams are unique to humans, but many dog owners will likely disagree. They have noticed that their dogs at various times during the sleep may shake legs, snort (哼) and sometimes growl (低声吼叫) which gives the impression that they are dreaming. These things may wonder us about whether dogs dream.

Scientists confirm that dogs probably do dream. It turns out that dog brains and human brains have many similarities during sleep cycles. Researchers used special machines to measure electrical activity in a dog’s brain and a human’s brain. Scientists already knew that when humans dream, a certain part of the brain is active during sleep. Researchers discovered that the same part of the brain is active in sleeping dogs. Scientists have other data that back up these findings.

Many people dream that they are trying to move but cannot. Interestingly, part of that experience is not a dream. When people sleep, the brain produces a chemical that causes the dreamer to become temporarily paralyzed (使麻痹). Researchers think this happens so that people cannot physically act out dreams while they are sleeping. Dog brains make the same chemical. In one study during which this chemical was blocked, sleeping test dogs performed physical activities, such as standing up, sniffing around the room for imaginary rabbits, or chasing imaginary balls.

Because of these similarities, researchers believe that the content of a dog’s dream might come from the same source as a human’s dream. “People’s dreams are usually based on things they did that day,” says Dr. Samantha Hudspith. “So we have reasons to believe that dogs dream about the things they’ve done that day. Of course, there will never be a way to prove this. Dogs cannot describe their dreams the way that humans can.”