Our family recently adopted Foster, an 8-year-old rat terrier, and on his second Sunday with us, we noticed that Foster was not himself. He had little interest in his principal joys, walking the neighborhood and chasing balls. Mostly, what he wanted to do was sit. We wondered if our new pet was OK, but by the next morning, Foster was up to his usual tricks.

It seems that the newest member of our clan had passed a busy week of adjustment and simply wanted to rest. In short, our dog was dog-tired.

That expression, “dog-tired,” is a curious fixture of our language, suggesting that canines are somehow the exemplar of fatigue. But maybe dogs aren’t more tired than the rest of us, although they may have a wiser sense of when they need a break.

I was reminded of this four years ago in a book by Jon Katz called “Dog Days.” Katz has made a cottage industry of writing about dogs, and in “Dog Days,” the author recounts his life with pooches and other animals at his farm in upstate New York. Among other things, Katz explains the origins of the term “dog days” in ancient astronomy.

The star Sirius got the nickname “dog star” because it belongs to a larger group of stars thought to resemble a hunting dog. Sirius is most visible in the night sky in July and August, and because the star is so bright, the ancient Romans thought it produced the extra heat that made the summer so sultry. Equating Sirius with summer led to the season’s nickname, “the dog days.”

Katz tells readers that animals seem better able to accept the dog days of summer than people are. “On these long, sweaty days, my animals slow down, move less, become markedly more nocturnal,” he writes. “The sheep and donkeys graze in the early morning cool, then hole up in barns and under trees for most of the day.”

Katz suggests that people could learn a thing or two from the way that animals handle August. “Maybe it’s good to slow down for a while, to wait out the summer and spend more time sitting on the front porch, to conserve oneself,” he adds. “Winter is really just around the corner. We will need all the energy we can save.”

Rest isn’t a natural impulse for most of us right now. The school year has resumed, and family calendars are already starting to thicken with appointments, campus programs, the personal and professional obligations of a household returning to its autumn routines.

We find shame in standing still, which is why any president gets blasted by critics each summer when he takes a vacation.

What we forget is that the mental and physical renewal required to do important things must come from letting the mind and body be quiet for a spell.

I’m trying to learn that. Foster already knows what to do when you’re dog-tired.