Veteran campers and hikers know the drill, especially those in areas where mountain lions roam. And anyone who doesn't need only consult the Web site of the California Department of Fish and Game for the best tack to take if he or she happens upon a big cat while communing with nature: "Do not run from a lion," the site advises, warning that "running may stimulate a mountain lion's instinct to chase. Instead, stand and face the animal."

But is it really safer to stay put than flee?

Not necessarily, says a new study, which warns that standing still may up one's risk of becoming mountain lion chow.

Richard Coss, a psychology professor and expert on the evolution of predator–prey relationships at the University of California, Davis, studied the behavior of 185 people who were attacked by mountain lions (aka pumas or cougars) between 1890 and 2000 in the U.S. and Canada. His findings, reported in Anthrozoos: A Multidisciplinary Journal of the Interactions of People & Animals:  half of the 18 people who ran when they were attacked escaped injury. The study also found, however, that those who ran had a slightly higher chance of being killed in an attack—28 percent (five) of those who fled died as a result of injuries, compared with 23 percent (eight) of those who remained motionless during big cat attacks. About 39 percent, or 28 people, who moved away slowly when approached by a mountain lion escaped without injury.

On the other hand, people who froze were the least likely to escape injury when a mountain lion attacked. Only 26 percent of them escaped. They also had the greatest frequency of severe injuries: 43 percent of those who stood still in the face of a lion were badly injured compared with 17 percent of those who fled, according to the study.

"Immobility may be interpreted by the mountain lion as a sign that you are vulnerable prey," Coss tells, adding that not moving could lead the predator to think you're not aware of its presence or are incapable of escaping. Staring down a puma can let the animal know you’re aware it’s looking, though distance can reduce its effectiveness.

Thus, running might be the smartest move, Coss concludes, particularly if you are in a situation that allows you to sprint in a sure-footed fashion. Running on uneven ground such as rocky terrain or snow could make it seem like you're limping, and mountain lions might consider you more vulnerable, Coss says.

Many wildlife organizations suggest standing one's ground defensively and even attempting to intimidate a mountain lion by shouting or throwing rocks. But Coss says that might not be as effective for pumas as for other wild animals, such as African lions and leopards. The reason, he says: those creatures co-evolved with humans over the past million years, whereas mountain lions have been exposed to humans for just thousands of years—too short a span for natural selection to enhance puma caution.

"I was surprised by the numbers," says Kathy Etling, an outdoor writer in Missouri who collected much of the data for the study to write her book, Cougar Attacks: Encounters of the Worst Kind, published in 2001. "If you’re a good runner, and you have a clear path then perhaps running is the best way. I don't think I would run. I'm not a particularly fast runner. I'm sort of clumsy. I would probably fall." She adds that turning your back to a cougar might be risky because many of them target the spinal cord when attacking their prey—and so might be tempted to lunge.

Through her anecdotal research, Etling found that hitting the animal with a walking stick or a gun butt often saved people from attack. She says that perhaps the best advice is to stick with a group; that sharply reduces the risk of attack, because animals typically target lone prey who have no chance of backup support from a herd.

Coss says he and his colleagues did not did not study mountain lion encounters or near-attacks because they wanted to get a handle on the best way to put off a lion bent on attacking.