We were not a one-dog household. The grief at Lyra’s passing had been profound, but the emptiness had been worse. Eventually, the entire family, including Callie, once again took a trip to the animal shelter. This time, Callie was there to help pick a new dog to join the family.

Walking down row after row of barking dogs, Callie look-alikes were everywhere. It seemed that every cage held a gaunt village dog. Black fur, white chest, tail in a C. And every single one had the breed listed as pit bull terrier mix. A feist by any other name. The temptation was strong to get a twin for Callie, but Helen insisted on a puppy. Something soft and cuddly—like Lyra, but different.

We zeroed in on a fluffy brindle puppy. He had a long snout and droopy lips and floppy ears that were too big for his head. No doubt about this one. He was a hound. Unlike his neighbors, he wasn’t barking. I crumpled up a piece of paper and tossed it in the corner of his pen. He bounded over to it and brought it back to me. This was supposedly the single best test of puppy temperament. A puppy that retrieved an object indicated a predisposition to work with humans. I was sold.

Callie gave him a good sniffing and wagged her tail. It was unanimous.

Continuing our tradition of literary names, Helen and Maddy called him Cato, after the character from Suzanne Collins’s The Hunger Games. Never mind that Cato was the most dangerous enemy to Katniss Everdeen, the heroine of the novel. At least he was bold and single-minded of purpose.

Our Cato, though, was a goofball. Gangly and awkward, he ran around the house, tripping over his feet and doing somersaults. Because of his penchant for putting everything in his mouth, he was dubbed the “fur ball with teeth.”

By the time Cato was six months old, his personality had begun to emerge. He seemed to move through the teething stage without too much destruction, although he had an obsession with the tags on clothing. He also liked to unravel toilet paper rolls and drag a trail of paper out of the bathroom.

Kat noted the eerie similarity to Newton.

“I think Cato is Newton reincarnated,” she said. “Those are the exact same things Newton used to do.” She was right. Even though Cato had been, in some way, a replacement for Lyra, he was closer to being a new Newton.

Helen, now thirteen years old, wanted to be primarily responsible for raising Cato.

“Do you know what that means?” I asked.

“I will have to let him out at night until he is housebroken.”

“Yes.”

“And I will have to train Cato to sit and stay and walk.” Cato heard his name and jumped into Helen’s lap. He started licking her face.

“You will feed him?” I asked.

“Uh-huh.”

“And you will pick up his poops on walks?”

Helen hesitated and thought about it. “Umm, I don’t know about that.”

I signed up Helen and Cato for puppy class at CPT. Mark’s class was a gentle introduction to basic training for both puppies and owners and let the puppies socialize with other dogs in a safe environment. Helen beamed in delight when she learned how to get Cato to sit and lie down. Like Callie, his love of hot dogs made training a breeze.

Of course, there was more to raising a puppy than basic training. If I had learned nothing else in the Dog Project, it was how to communicate better. Dogs come ready-made to soak up the social rules of the household. It was our human inconsistencies that made it difficult for them.

Humans emit a constant stream of signals. We talk constantly. Our bodies are in motion. We wave our hands in wild patterns in feeble attempts to communicate emotions. It isn’t at all clear how much of this verbal and physical chatter is actually necessary. I realized that Callie ignored most of the family’s gesticulations, instead reserving her attention to the signals that carried useful information. I respected her regal demeanor. What, two years ago, I had mistaken for aloofness, I now understood to be an economy of attention. She had revealed herself to be capable of great feats of mentalizing when working with me as part of the Dog Project. If she wasn’t interested in what I was saying, I realized that it was because I wasn’t being clear in what I wanted.

After spending hours staring eyeball-to-eyeball with Callie, we had achieved a level of communication that I don’t think I had ever had with a dog. Not even Newton. I had learned to read some of Callie’s body language, especially her eyes. Her flicks of attention telegraphed what caught her interest. The photographs and video footage from the Dog Project made it obvious that the dogs’ attention was focused on the humans. I hadn’t noticed it at the time, but when I replayed the footage, it was impossible to ignore. The dogs were watching us, trying to figure out what we were thinking and how to shape their own behavior to fit in.

Consistency and clarity. That was the ticket. I resolved to be more consistent—with both dogs and humans alike.

After one of the puppy classes, Helen asked me, “Could Cato be in the Dog Project?”

“He’s too young,” I replied.

“How old does he have to be?”

“At least a year old.”

“But,” Helen opined, “he’s really smart. I bet he could hold his head still.”

“He probably could. But puppies’ brains aren’t fully grown. We wouldn’t know how to compare his brain to an adult brain like Callie’s.”

Helen took this in. “Could I start training him so that he’ll be ready by the time he’s one year old?”

“Sure,” I said. “But why do you want him to be in the Dog Project?”

Helen stroked Cato’s head. “So I can know what he’s thinking.”

I smiled. I knew exactly how she felt.

Epilogue

Two years and two dogs. Two dogs scanned and two dogs gone. The Dog Project started as an idea born from the grief of losing our pug Newton but blossomed into something bigger than any of us could have expected. Up until that point, I had kept my feelings toward dogs mostly to myself. But after we published the initial results with Callie and McKenzie, there was an outpouring of support from people all over the world. I was moved by how strongly people wanted to know what their dogs were thinking.

One of the first people I heard from was Jessie Lendennie, a poet and managing editor at the publisher Salmon Poetry in Ireland. Jessie was kind enough to send me an anthology of poems, Dogs Singing, that she had compiled from poets all over the world. It is a remarkable tribute to the powerful effect that dogs have on people. I found it inspiring as the Dog Project progressed beyond just two dogs.

Moving forward was a risky move. We still had no funding to speak of. The only reason we got as far as we did was through the volunteer efforts of Mark and Melissa and all the people in my lab, especially Andrew. Scanner time still cost $500 an hour, and there were no freebies in that department. I had paid for scan costs out of discretionary research funds that I had accumulated over the years, but at the end of the hot dog and smell experiments, we had to ask ourselves: What now?

We had the only dogs in the world that were trained to go into an MRI. We could keep dreaming up questions to ask about how the canine brain worked, but there were limits in what we could learn from just two subjects. If the Dog Project was to continue to decipher what our furry friends think about us, the path was clear: we needed more dogs. If we had more dogs, we could sort out the questions about how many of the differences between Callie and McKenzie were because of their genetics, their environment, or just random day-to-day fluctuations in their mood, which surely must happen, just like humans. We all wanted to know about the differences in breeds.