Groupers, a warm-water fish in the sea bass family, hunt for food together with wrasse and giant moray eels. If during a chase, the intended prey slips away into a hidden crevice, the grouper sometimes assumes a vertical position directly above the hiding place, then shakes his or her head repeatedly.

Groupers do this, University of Cambridge zoologist Alexander Vail and his colleagues discovered, when their hunting partners are positioned in such a way as to notice the signal. The communication is effective: the partners often respond by immediately exploring the indicated niche.

It’s a neat example of what’s called referential signaling, a kind of smart purposeful communication that may be viewed as surprising in fish—and thus also an example of a “food animal” showing us that they think.

In this, the groupers aren’t alone. An explosion of scientific studies in the last decade reveals that many animals who grace our tables both think and feel as they go about their days. From scientific study, we may not always be able to discern with precision what they think or feel, yet their behavior leaves clues strong enough to withstand charges of anthropomorphism, the wishful projection of human qualities onto other animals.

As science writer Brandon Keim has put it, “What once was considered anthropomorphic thinking is now mainstream science.” I’d add that science is finally beginning to embrace animals who were, for a long time, considered second-class citizens.

As Annie Potts of Canterbury University has noted, chickens distinguish among one hundred chicken faces and recognize familiar individuals even after months of separation. When given problems to solve, they reason: hens trained to peck colored buttons choose 9 percent of the times to give up an immediate (lesser) food reward for a slightly later (and better) one. Healthy hens may aid infirm friends, and mourn when those friends die.

Pigs respond meaningfully to human symbols. When a research team led by Candace Croney at Penn State University carried wooden blocks marked with X and O symbols around pigs, only the O carriers offered food to the animals. The pigs soon ignored the X carriers in favor of the O’s. Then the team switched from real-life concrete objects to T-shirts printed with X or O symbols. Still, the pigs ventured only toward the O-shirted people: they had transferred their knowledge to a two-dimensional format, a not-inconsiderable feat of reasoning.

I’ve been guilty of biased expectations, myself. At the start of my anthropology career almost four decades ago, I was firmly convinced that monkeys and apes out-think and out-feel other animals. They’re other primates, after all, animals from our own mammalian class.

Fairly soon, I came to see that along with our closest living relatives, cetaceans too are masters of cultural learning, and elephants express profound joy and mourning with their social companions.

Long-term studies in the wild on these cerebral mammals helped to fuel a perspective shift in our society: the public no longer so easily accepts chimpanzees or monkeys made to undergo painful invasive procedures in biomedical laboratories; elephants forced to perform in circuses, and dolphins kept in small tanks at theme parks.

Over time, though, as I began to broaden out even further and explore the inner lives of fish, chicken, pigs, goats, cows, and octopus, I started to wonder: Will the new science of “food animals” bring an ethical revolution in terms of who we eat? In other words, will the breadth of our ethics start to catch up with the breadth of our science?

Animal activists, including vegetarians and vegans are already there, of course, committed to not eating these animals. But what about the rest of us? Can paying attention to the thinking and feeling of these animals lead us to make changes in who we eat?

One set of clues comes from Esther the Wonder Pig. Esther lives in Ontario, part of the family of Derek Walter and Steve Jenkins. In 2012, when the two men purchased Esther, she was advertised, falsely, as a micro-pig. Now at 650 pounds and a viral social media star, she conveys what’s clearly a vital inner life of preferences (to open the door on her own in order to relieve herself outdoors) and pleasures (cuddling, and frozen mango smoothies) in her daily life. In an interview, Walter and Jenkins remarked that “hundreds and hundreds” of people contact them to say that because of Esther they no longer eat pig products Esther brought home to them the connection between pork and bacon, on the one hand, and a sentient, fun-loving personality on the other.  

Beyond anecdotal information along these lines, though, do hard data exist on this question?

In one study, a research team led by Boyka Bratanova at the University of Surrey told American study participants one of two narratives about tree kangaroos living in Papua New Guinea. When they were told that tree kangaroos are consumed as food in that region, people judged the kangaroos to be both less capable of suffering and less deserving of moral concern than when they were told only that the animal dwells in that region.

It may be deeply uncomfortable to reflect on eating savvy creatures who express their emotions. My strong suspicion—which I hope will be tested as a hypothesis—is that some people will decrease their meat and fish intake as they learn more about who they are consuming. That’s one reason I spent the last three years writing Personalities on the Plate: The Lives and Minds of Animals We Eat. I believe that knowledge of animal cognition and emotion gives those of us lucky enough to have few constraints on our food choices yet another reason—along with concerns for our health and that of the planet—to reduce or eliminate our intake of meat, and to eat more plants.