①Happy as a pig in mud. It's a funny saying, isn't it? For much of the past century, scientists thought non-human animals didn't have emotions. But recently, we've learned that they're more intelligent than we thought and they do have emotions.
②Frans de Waal, a primatologist at Emory University, believes that many animals feel fear, pride, hope, joy, and happiness. However, they don't experience these emotions the same way as we do. "We can observe animals and guess how they feel or look at their hormones (激素) and see if they're stressed, but we can't really know how they feel inside—we're just making our best guesses." says Fay Clark at the University of Bristol. So, how can we tell what they're feeling inside more scientifically?
③To better understand animals, scientists started looking at animals' faces. Researchers have found that horses, cows, and rabbits make certain facial expressions when they are in pain. Sara Hintze of the University of Natural Resources says that positive emotions are harder to read, but researchers are beginning to explore the signs of positive emotions and there's still a lot to learn.
④Researchers have had more success with vocalizations. In a study from 2022, one scientist, Elodie Briefer, and her team made a computer program to tell whether pigs' noises are negative or positive. They used more than 7000 recordings from different situations. In situations thought to be positive, such as when pigs were running free, eating, or expecting a reward, they usually made sounds like grunts and barks. In negative situations, such as when they were fighting or being handled by humans, their grunts and barks were longer and deeper, or they made loud squeals and screams.
⑤ These new findings help start campaigns (运动) to move from just stopping animals suffering (受罪), to doing everything we can to make sure they live happy lives. This is especially true for animals living on farms or in zoos. Briefer says that people will soon realize that understanding animals' feelings is an important part of caring for them, maybe even as important as their health.
B . 
C . 
D . 
