After a woman in Virginia was reportedly mauled to death by her own dogs, some of her friends had trouble believing the story, because the woman had a strong bond with her dogs.

But what could cause a dog to turn on its owner?

The 22-year-old woman, Bethany Lynn Stephens, was found dead in the woods last week, with her two dogs apparently "guarding" her body, according to the Washington Post. Authorities who found the body described a gruesome scene: the damage to the body “was so extensive that there was nothing left to compare bite marks to," Jim Agnew, the Goochland County sheriff, said in a news conference. Bite marks on the body confirmed that the dogs attacked Stephens, and Agnew also said he and the other officers observed the dogs eating Stephens' body. Family and friends said Stephens had raised the dogs since they were puppies and that they were affectionate.

Experts say there's no way to know for sure what caused this attack.

"It's a difficult incident to understand. It certainly is horrible," said Richard Polsky, an animal behavior and dog-bite expert in Los Angeles. "We just don't have enough information to understand why these two dogs turned on this owner," Polsky said. [Infographic: Dog Bite Incidents]

But in general, for dogs to act aggressively, there needs to be some kind of external "trigger," Polsky said. One possibility is that, while Stephens was walking the dogs, something out of the ordinary happened; for instance, the dogs sensed "prey," like a rabbit or squirrel, and tried to go after it. If Stephens interfered with the dogs while they were going after prey, they may have redirected their aggression toward Stephens, Polsky said. "The dogs may have been thwarted in doing something, got frustrated and turned around and attacked the owner," Polsky told Live Science.

Ron Berman, a dog-bite expert and certified forensic consultant, agreed that this could be a scenario in which dogs attack their owner. "Usually, you have some initial aggression, the human tries to stop the aggression, the dog reacts to that," Berman told Live Science.

Berman added that it's possible Stephens' dogs were not fed well, because dogs don't typically try to eat a human body after an attack, unless they haven't been getting enough food.

Officials noted that lately, Stephens' dogs had been living with her father, who kept the dogs in a kennel outside; and the animals had little human contact besides occasional visits from Stephens.

Rather than both dogs attacking Stephens at once, it's more likely that one dog initiated the attack, and the other joined in, Polsky said. It's also possible that the dogs had shown signs of hostility before, but these signs were overlooked, he said.

There are about 5 million dog-bite cases annually in the U.S., Polsky estimated. Around 30 to 40 people die each year from their injuries, and an estimated 100,000 are injured badly enough to require plastic surgery or extensive suturing, according to Polsky.

Most fatal dog attacks involve pit bulls. (Officials identified Stephens' dogs as pit bulls.)

But Polsky stressed that this doesn't mean all pit bulls are inherently aggressive. Some pit bulls have been bred for fighting or intimidation, and so they may have more aggressive traits. But studies show that Chihuahuas and Jack Russell terriers are actually the most aggressive breeds, but their size and physical limitations prevent them from killing people, Polsky said.

"Unfortunately, an incident like this just reinforces people's beliefs," that all pit bulls are dangerous, Polsky said. "It's just not fair. I come across a lot of pit bull dogs that are just the sweetest dogs in the world," he said.

To help prevent attacks, Polsky recommends educating children not to run up to a dog they don't know. (Most dog-attack victims are children, and most dog attacks are caused by males, Berman said.)

If someone wants to own a pit bull or Rottweiler, they should go to a reputable breeder who has "bred their dog for docility rather than just looks," Polsky said.

Editor's Note: Live Science editor Tia Ghose contributed reporting to this article.

Original article on Live Science.