When the rats are brought into the room, Jonathan Balcombe lights up. "Hello," he says warmly to one, carefully picking her up and looking into her eyes. "Just look at that nose going. It's an olfactory world for them. She's taking in all the smells."
Balcombe, a research scientist with the US-based Physicians Committee for Responsible Medicine, has an obvious empathy for the rats. They remind him how much he misses the three he once kept as pets. He dips a finger in his glass of water and offers it to the rats who gratefully lap his fingertip.
"They're great lickers too. I confess I've French kissed my rats quite regularly. I would put food in my mouth and let them look inside and take it out." Disturbing. But from Balcombe's point of view, he's helping to redress the bad rep rats have.
Balcombe wants to show rats, stigmatised as filthy pests, are inquisitive opportunists, naturally sociable, and that they make excellent companions.
Not only do they love to play it seems they also have a sense of humour. Balcombe, in New Zealand on a speaking tour promoting his book Pleasurable Kingdom: Animals and the Nature of Feeling Good, refers to a recent discovery that rats "enjoy" being tickled.
The notion comes from the research of Jaak Panksepp, who measured ultrasonic squeals associated with tickling and petting, and found rats squealed seven times more while being tickled.
He also noted that other rats reacted positively to the high-pitched chirps, learned to recognise when they were about to be tickled and ran across the cage faster in anticipation.
So rats can laugh? "I call it mirthful behaviour," says Balcombe, who agrees it's difficult to ascribe laughter or humour to animals without succumbing to sentimentality or anthropomorphism.
"It's a good one to challenge. There's not a wealth of data out there on humour. It's almost all anecdote. There is no one who has set out to do a study of humour in a non-human."
Then he'll recount a series of anecdotes - about a sign language-trained gorilla using word play, about chimpanzees' panting laugh and a sharp burst of sound dogs make when playing that some researchers say is the canine equivalent of laughter.
And there's animal mischief - like the dusky dolphins which have sneaked up on kelp gulls resting on the surface, grabbed the birds' legs and dunked them before letting go. Or the octopus who took to squirting water at a visiting lecturer and photographer.
More examples are recounted in Pleasurable Kingdom in support of the thesis that animals have emotions and consciousness. In short, animals are sentient beings like us.
For anyone who has pets, this is not surprising. I know by his muffled yelps that my English bull terrier Trick has dreams - as though being chased or perhaps chasing something.
I know, too, when my ocicat Sheba wants to play the biting-the-hand game because she climbs up on the couch and bats the TV remote out of my hand.
But Balcombe pushes the envelope of what animals can feel. Love and sex, just because they feel good, may not be too much of a leap. Moral obligations and transcendent emotions, including aesthetic appreciation, are surely a bridge too far.
"Animals have a sense of beauty," he insists. They have an appreciation for things that are appealing to the senses, be it taste, smell, sight or sound.
"When birds sing we find it beautiful. I would say so do they - it resonates with them."
Balcombe says advances in ethology (the scientific study of animal behaviour) are gradually ticking off the list of previously unimagined things animals are capable of, breaking down traditional distinctions between animal and human.
"Animals can't build bombs or computers, for that matter." And they can't have a religious experience, can they? "That one I would contest," says Balcombe, as long as religious is defined as spiritual, ethereal or beyond the conscious world.
He cites the instance of a chimpanzee so engrossed in a beautiful sunset that he forgot to pick a paw-paw for his evening meal. Then there were the chimps seen to perform an elaborate dance when encountering a spectacular waterfall.
Balcombe agrees two anecdotes do not a case for animal religion make, but he argues if scientists purposefully documented and studied the possibility that animals can have religious experiences, there would be interesting results. He would be surprised if some great apes didn't have the ability.
Balcombe pushes the boundaries, too, on what type of animal is sentient. Fish, long considered dumb and numb creatures with simple reflexive reactions, feel pain and pleasure. Cue more examples of experiments and observations, such as varieties of cleaner fish and their complex relationships with their clients.
Balcombe says the biggest problem fish have is their lack of facial expression, which makes it harder for people to empathise with them.
He describes the common sight on wharves where people are fishing - a bucket of fish with not enough water and the fish flopping about suffocating. "If these fish were screaming and they had horrified looks on their faces, I imagine I would encounter that scenario a bit less."
In his book, Balcombe wonders, too, whether insects have feelings, describing a time when he stopped to give a downed spicebush swallowtail butterfly a drink.
Does he know when he developed his empathy for creatures? "I think from birth. I think deep in me I have a close affinity and concern for animals. In my earliest memories I was very sensitive. Kids stepping on caterpillars would really upset me. I would tell them what I thought."
This sensitivity led him to become a vegan at 24, a decision he made just before a solo, three-month bird-watching tour around India.
Still a vegan and avid birdwatcher, he relates a moment of "absolute unbridled pleasure" when walking through Cornwall Park in search of tui, which had so far eluded him on his New Zealand visit.
"I was feeling the breeze on my legs. I felt physically good and then I saw tui for the first time. I saw their lovely little white tufts. It was a lovely moment for me." Singular sentience.
Balcombe argues sentience is adaptive. Being able to feel pleasure is in line with Darwinian natural selection because it encourages good, survival behaviour. But rather than explaining all animal behaviour in evolutionary terms, Balcombe advocates bringing experiential evidence to the table.
Hence his unashamed gathering of animal anecdotes and willingness to talk about what's observed in anthropomorphic terms, such as animals feeling happy or experiencing pleasure.
He has been criticised for this position. As Marian Stamp Dawkins, professor of animal behaviour at the University of Oxford, says of a picture in Balcombe's book: "The caption could have been 'Red kangaroos copulating'. In fact it is 'Red kangaroos enjoying sex'." At his lecture at Unitec's School of Natural Sciences, Balcombe shows the same picture, but with a black censoring strip over the kangaroos' eyes as if the pair has been snapped in public in a lewd act.
Behaviourists like Dawkins argue that the existence of conscious feelings cannot be tested empirically, so the study of conscious emotions is outside the realm of science.
"The privacy of experience is always a challenge," agrees Balcombe. "It's irresolvable, you cannot feel another's feelings. But it doesn't follow that we have to be terminally agnostic about the questions of animal emotions."
Logically Balcombe's position - animals feel and have a quality of life that's rich and worth living - leads to vegetarianism. But although he eschews meat, dairy products and eggs, Balcombe sees it as a choice informed by science and ethics.
"I can't stop sheep farming. I can't stop mulesing [surgery to sheep tails] or farrowing crates, or the battery cage. If I could, I would, but it doesn't mean I don't care about the farmers and their careers. You've got to consider all those things. But I can personally stop contributing to that."
While the line of what not to eat is clear for Balcombe, he concedes it is possible, albeit difficult, to produce eggs or milk in such a way as to not harm animals.
"If the dairy industry shared the milk with the calf, I can envision a way. But in most cases it's going to be a violation of the animal's normal existence. That's where I say that's problematic and I would rather we weren't doing it."
He agrees the ethics of animal rights can be thorny. On transplanting pig islet cells into humans to treat Type 1 diabetics, he admits there's no easy answer.
"It speaks to the conflict of rights - the rights of the diabetic and the rights of the pig."
He also has ethical problems about the feeding of his two cats he "has the pleasure of being owned by" in Washington, where he lives with his wife and daughter. Is feeding them meat a problem?
"Absolutely, but the cats didn't ask to live with vegan humans - though I believe they have a good life with us. We do feed them canned meat, but I combine it with a commercial vegan cat formula, both dry and wet. I like to think more variety keeps things more interesting for them palatability-wise."
Balcombe's new project is a documentary to showcase little-known aspects of animals' perceptiveness, sociability, intelligence, virtue and sensitivity. He's on the hunt for footage he hopes will get viewers to think about their own and humanity's current relationship with other animals.
"Our treatment of animals is profoundly out of step with what we now know about their sensory capacities and their experience of life. They are as sentient as we are."