Groucho Marx once said, "Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read."
But it is beginning to get lighter in there, thanks to modern cognitive science.
Groucho's quip graces the opening page of "Inside of a Dog: What Dogs See, Smell and Know," a new book by cognitive scientist and psychologist Alexandra Horowitz that goes a long way to suggest what it's like to think with a dog's brain -- to actually be a dog.
Combining new knowledge from hundreds of scientific and animal behavior studies, and mixing it in with a fine style guided by her own loving bemusement of dogs -- especially of her own Finnegan, rescued as a sick and needy pup from a shelter -- Horowitz gives us a fascinating picture of a dog's umwelt (OOM-velt) -- German for "their subjective or 'self-world'."
"Umwelt captures what life is like as the animal," she says.
We met Horowitz and Finnegan on a high plateau -- a grassy field hidden amid a circle of trees in New York's Central Park -- one day at 8 a.m.
There was one hour to go before leash laws came into effect, so we were surrounded by some two dozen joyous dogs of every size, shape, color and pedigree -- or lack thereof -- and as many wakening humans.
Racing around, sniffing, forming little groups and making up games, the liberated dogs turned it into a scene much like any elementary school playground, brimming over with the invention of play -- but play on steroids.
We more static humans stood in their midst, wrapped for a while in dog time.
"Actually, dogs see faster than humans, so to speak," Horowitz, who teaches psychology at Columbia University, told ABC News.
As she spoke, her own Finnegan -- now a fully grown jet black streak of a dog -- zoomed around the outer edge of the field, inveigling a few other dogs into some sort of high-speed canine game of catch-me-if-you-can.
"They have what's called a higher 'flicker fusion rate,'" she said, Finnegan's leash dangling from her hand.
"We see a certain number of what you might call snapshots every second -- maybe about 60 snapshots a second. Dogs send about 70 or 80 images per second, which means that they're seeing a little bit more in every second, a little bit faster in every second than we are.
"Say, a Frisbee; they might see its vector towards its head -- mouth -- a split second before we do."
A human-canine game of Frisbee-catch that illustrated exactly what she was talking about was just taking place out in the field.
A happy dog raced in a blur after a very long throw, and with brilliant split-second timing, leapt into the air, catching up with the airborne spinning plastic disk and grabbing it in its teeth just before it would have hit the ground -- and, the moment it touched down, spun on a dime and headed eagerly back to the thrower.
"At Frisbee, the dog will have you beat every time," she said.
Horowitz also explained how, as she put it, dogs can "smell time."
"Odors exist in different concentrations," she said, as a rumpled white bulldog on the loose started sniffing intently around our feet.
"Tracking dogs can effectively follow an odor path by noticing the difference in concentration from, say, the left footprint to the right footprint," she said.