“Lessons From Lucy: The Simple Joys of an Old, Happy Dog” is the title of Dave Barry’s new book. It’s about what an aging Barry, one of America’s finest humorists, learned from his aging mutt. In writing it, Barry managed a rare thing: a humorous dog book that is also useful. As you read, it gets even rarer: a useful, humorous dog book that examines the lessons of gratitude that apply to man and beast.

We talked with Barry about barking at trash haulers, the improbability of cat parks, dogs in space and, of course, Lucy, whom he describes in his book as “a low-lying cloud that is constantly drizzling little black hairs.”

Q: What lesson did you learn from a member of a different species that cannot form words and loves to roll around in mud that is soaked with squirrel musk?

A: The lesson I most enjoy attempting to apply is having fun. I’m too old to really have fun just for the sake of fun. I need an excuse. So, I want to play in a rock band not because it’s fun, but because it’s an important life lesson I learned from my dog.

Q: Lucy must appreciate seeing you apply her fun-imperative lesson, right?

A: When I play the guitar Lucy immediately gets up and leaves the room. She doesn’t have the authority to pull the plug, but if she did, she probably would.

Q: What else would she do if she had more authority?

A: The garbage man would be dead. Because he is taking the garbage without her permission.

Q: Lucy’s right, by her laws. There something buried deep in the nature of dogs that wants to protect. We tend to deny that, don’t we? Talking baby talk to our dogs, “Aw widdle fwufums is so sweet.”

A: That’s why I don’t buy the “fur baby” thing. They’re just wolves that have adapted to a new pack, with all the great traits of loyalty and companionship. But they’re still wolves. They have powerful and violent defensive urges. If you’re going to buy the “incredibly loyal to me” part you have to buy where it came from, which is the wolf pack part of the dog.

But I genuinely get that dogs are not just animals. There’s a soul there. But I also get that if I were to give Lucy to someone else, within a short period of time, she’d be just as bonded to whoever that was.

Q: Sensitive question. Lucy is still with us, right?

A: Lucy is still here, she’s now 11. She looks very old, a lot of white in her face. A lot of people told me that that was the first thing they worried about, that Lucy would die in the book. Not mine.

Q: Oh, I’m relieved to hear that. We can take a lot of human sadness, but the sadness of dogs seems unusually hard to bear. In the HBO show “Chernobyl,” the episode that involved the shooting of the irradiated dogs was the hardest for viewers to bear.

A: It seems like it’s OK to have people turn into human shish kebabs, but don’t harm the dogs! Dogs are innocent, and they seem remarkably vulnerable.

Speaking of “Chernobyl,” it can’t have been great to have been a Soviet dog. Laika, the first dog in space, it’s a sad story. But you know you can only get a dog into space. “Here, boy, we’re going to go. For a ride, yes!” You try to put a cat into space, its talons would drip with the flesh of Soviet scientists.

Q: Is your book full of anti-cat propaganda? Readers should be warned.

A: I love dogs a lot, and I do not love cats a lot, and I got challenged repeatedly by my cat-loving son. I would just say everyone knows what a dog park is: dogs playing, people talking happily about their dogs. Imagine a cat park. Vast empty space, people 30 or 40 feet apart, saying, “Where’s my cat?”

Q: Your book details the lessons Lucy has taught you. Is there a lesson you wish she would learn?

A: Yes. That when I leave I am coming back. This would probably ruin the dynamics, but if I could explain that I’m coming back, if I could go out the door knowing she knew that for sure, it would better for us both.

Of course if she did know, she might not be so happy to see me when I come back.