Man's best friend is friendlier when a woman is holding the leash, according to a new study out of the Czech Republic. The study, by Petr Rezac and his colleagues at Mendel University in Brno, looked at about 2,000 interactions between dogs during their walks in 30 different areas of their city, cataloging the effects of age, sex, size and other factors — including who was taking the dog on the walk. The study will be published in the journal Applied Animal Behavior Science. Here's an early look at some of the more surprising findings:

1. Dogs are more aggressive when a man is walking them
When it comes to a dog's relative pugnacity, the gender of the person walking him is the most important factor. Pooches being walked by a male were four times more likely to bite or attack other dogs than those walked by women, the study found. "The thought: Men tend to be more aggressive," says Rebecca Thomas at Phoenix's ABC 15 News. "Dogs are unusually skilled at reading human social and communicative behavior," Rezac explains, so the walker's "aggressive tendencies and/or impulsivity" may affect the dog's behavior.

2. The leash makes dogs more aggressive, too
Dogs tethered to a leash are twice as likely to threaten another dog as those running free, the study found. Why? "Leash aggression" is "most likely a reflection of the frustration dogs feel when the leash prohibits them from expressing normal greeting behaviors," the Humane Society's Inga Fricke tells Discovery News. Dogs like to run around each other when they first meet, explains Lisa Peterson of the American Kennel Club, and "they can't do this run-around behavior when on a leash and they likely feel more threatened."

3. Male dogs prefer the company of female dogs
Most common dog-dog interactions involve sniffing, and male canines prefer sniffing female dogs. The study also found that while female pooches enjoy playing with both genders, male dogs prefer frolicking with females. "That makes sense," Peterson tells Discovery News, "because females rear litters of puppies and must play with them. It's a nurturing thing so they are probably genetically predisposed to play more" and not discriminate between genders.

4. Puppies are way more playful than older dogs
Though this finding is not exactly groundbreaking, Rezac and his colleagues were able to quantify the differences: Puppies play with one another more than twice as often as adult canines, and 11 times as often as doggy seniors.

5. Walks are good for people but great for dogs
Walking your dog can literally save its life, according to a study presented in 2010 by dog-walking researcher Rebecca Johnson at the University of Missouri. Johnson's team conducted a study of dogs at shelters: Half were randomly selected for five walks a week by elderly human volunteers, while the canine control group "sat glumly in their cages," says Hal Herzog at Psychology Today. "The results were impressive," if sad for the control group: 75 percent of the walked dogs were adopted into permanent homes, versus 35 percent of the not-walked; 9 percent of the walked were euthanized, compared with 27 percent of the control group. Elderly dog-walkers benefit, too, according to Johnson. They become fitter and healthier than those who don't walk, and even those who walk with human friends.

Sources: ABC 15 NewsANIDiscovery News, One Green PlanetPsychology Today