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.
Another trick the researchers report seeing is the bark-and-grab: a dog will suddenly jump up behind a person in the street who is holding some snack, enough of a surprise that the food gets dropped for the grabbing.
The female we followed on the Kievskaya Line seemed at ease as she traveled among all the people packed in around her, and with reason: Moscow's subway strays even have their own statue in the Mendeleyevskaya station.
It commemorates Malchik, a stray who lived there until he was stabbed by a fashion model in 2002 who didn't like how Malchik barked at her terrier.
Learn How to Live With Them
Outraged Muscovites erected the statue. Passersby now rub the Malchik's shiny bronze nose for good luck.
Despite this public admiration for the strays and their survival skills, many Muscovites still see the tens of thousands of homeless dogs as a big problem.
"We have to solve it," Anastasia Markina of the Alliance for Animal Rights of Moscow said. "They're not guilty that they became homeless. We should solve this problem in a humane way."
There have been sterilization campaigns, and city dogcatchers manage to get some strays into pounds, but it's all had little effect on the overall stray population.
Vereshchagin thinks that Moscow's residents need to accept the dogs as a part of life in the city.
"It's not really easy to completely move the dogs out of the streets," he says. "I guess we just have to... learn how to live with them."
The stray dogs of Moscow - including those who use the subway - have themselves already done a lot to work for peaceful coexistence.