Many war-weary veterans of the Iraq War take kindly to the animals they meet abroad — some of them have even gone to great expense and trouble to bring dogs back home with them at the end of their tours of duty.
What, then, provoked one U.S. Marine to let himself be videotaped apparently flinging a yelping puppy over a cliff, bursting into laughter at the sound of the animal's body hitting the ground below? The tape of the apparent incident has rocketed around the Internet, provoking a firestorm of criticism.
The motivation for such an act, if it did indeed occur, may be as complex and deep as the U.S. war that has dragged on for more than four years, experts told ABCNEWS.com. Chief among them: Having to live with the constant fear of being injured or killed might have led this Marine to take his aggression out on a defenseless animal, several psychologists said.
"Most of the time war is about chaos and the fear of being wounded or killed," said David Spiegel, professor and associate chairman of psychiatry and behavioral sciences at the Stanford University School of Medicine. "And so you're constantly confronting those fears and one of the ways to confront that may be by showing you're the one that renders other creatures helpless."
"The thought is that 'I'm not the one who gets thrown off a cliff, I'm the one doing it,'" said Spiegel.
The clip depicting the puppy's horrific treatment garnered tens of thousands of hits on YouTube before it was taken down. The U.S. Marine Corps launched an investigation into the identity of the Marine after it issued a statement calling the apparent act "shocking and deplorable." The videotape's authenticity has not been verified by U.S. authorities.
How much time the Marines shown in the video served abroad is still unknown, but several mental health professionals told ABCNEWS.com that people who treat animals badly may act out because of their oppressive surroundings or sometimes as a result of the shock they might have suffered -- be it the horrors of war or an abusive parent during their childhood.
"There may be personality variables that predispose people to [harm animals]," said Allen Enton, the past president of the American Psychological Association's division of family psychology. "But it also may be somehow stimulated by some context like being in a group situation or feeling oppressed and down and wanting to just get back at the world."
Animals are easy targets for angry or disturbed people, said Enton, adding that not having to worry about the animal retaliating makes hurting it that much easier.
The Marines might tape the incident, including their laughter and indifference, when another commented how "mean" it was to the puppy, as an ego booster and a way to feel powerful and in control.
"Somehow documenting it is a way to show people 'look at what we did' and 'look at how brave we are and how strong we are,'" said Enton. "But you have to wonder what has caused them this kind of stress so that they have to react in such a violent way."
"They're on such a power trip about what they're doing that it doesn't dawn on them how disgusting it is," said Stanford's Siegel. "A person can get set to such levels of psychological arousal that ordinary life can seem kind of drab, and the only way to keep yourself feeling kind of good is to do things that are dangerous or anti-social."
Children who are violent toward animals -- killing a stray dog or cat, for example -- have a heightened risk to be cruel to people, said Scott Lilienfeld, a professor of psychology at Emory University.
"It's well established that one of the best predictors of later violence is cruelty to animals," said Lilienfeld, who declined to comment specifically about the Marines in the puppy video because he has never treated them. "For some kids, [harming animals] might give them an immature sense of power; they may get a kick out of seeing the animal suffer."
But in contrast to this latest incident, most kids would rather hide away and torture the animal, careful not to be caught by parents or adults, said Lilienfeld.
"It's going to be the kind of thing where nobody else is around -- kids know it's not socially acceptable," said Lilienfeld.
But even the worst kids don't always hurt animals, he said, which may demonstrate quite how much it takes to harm or kill a dog.
"Cruelty to animals is rare and frankly even a lot of bad kids love animals," said Lilienfeld. "Most people -- even callous kids -- have a strong immunity to really hurting dogs and cats. You've got to be really bad."
This trend also works in reverse, he added, meaning that individuals who harm or kill humans may also be more inclined to then hurt animals.
"One of the horrible problems is that we have men and women coming [home] who have participated in horrendous violence," said Stanford's Spiegel. "They've crossed the line [of violence] once, and it makes it easier to cross the line again."