Every so often, if you ride Moscow's crowded subways, you notice that the commuters around you include a dog - a stray dog, on its own, just using the handy underground Metro to beat the traffic and get from A to B.
Yes, some of Moscow's stray dogs have figured out how to use the city's immense and complex subway system, getting on and off at their regular stops. The human commuters around them are so accustomed to it that they rarely seem to notice.
"In Moscow there are all sorts of stray dogs, but... there are no stupid dogs," Dr. Andrey Poyarkov, a biologist who has studied Moscow's strays for 30 years, told ABC News.
As many as 35,000 stray dogs live in Russia's capital city. They can be found everywhere, from markets to construction sites to underground passageways, scrounging for food and trying to survive.
Taking the subway is just one of many tactics the strays have come up with for surviving in the manmade wilderness around them.
"The street is tough and it's survival of the fittest," says Poyarkov. "These clever dogs know people much better than people know them."
Poyarkov says that only a small fraction of strays have figured out how to navigate the maze that is Moscow's subway system.
What's most impressive about the subway dogs, says Poyarkov's graduate student, Alexei Vereshchagin, is their ability to deal with the Metro's loud noises and packed crowds, distractions that domesticated dogs often cannot handle.
"It's stressful even for people standing in a crowd," he says, "and the dogs are lying down so no one is seeing them, so anyone can put feet on them. But they get used to this."
ABC News found a female stray in the Kievskaya station, and barely managed to follow her as she zipped between the legs of the bustling travelers around her to catch a ride on the Koltsevaya Line.
Once on board, she settled down on the floor among the feet and legs, even dozed a bit, and occasionally got up for a brief conversation with a friendly human.
She seemed to sense that such close quarters were no place to appear threatening.
Author Eugene Linden, who has been writing about animal intelligence for 40 years, told ABC News that Moscow's resourceful stray dogs are just one of what are now thousands of recorded examples of wild, feral and domesticated animals demonstrating what appears, at least, to be what humans might call flexible open-ended reasoning and conscious thought.
Linden cites a wide variety of creatures ranging from captive orangutans and otters who frequently and slyly "trade" with their keepers, to a British cat famous for regularly taking the bus to a squirrel in Oklahoma who became a local hero when people began to notice that it regularly obeyed traffic signals when crossing a busy street.
"The take-away is that animals are not just passive in this," Linden told ABC News. "They are figuring out what we're about and how they can game the system, and work it to their advantage as well."
Moscow's strays have also been observed obeying traffic lights, says Vereshchagin. He and Poyarkov report the strays have developed a variety of techniques for hunting food in the wild metropolis.
Sometimes a pack will send out a smaller, cuter member apparently realizing it will be more successful at begging than its bigger, less attractive counterparts.