What is it about animal webcams? These stress-busting, smile-inducing sites are like an online yoga class, giving us a break from our daily routine of reading, writing and analyzing data while plugging our brains into monitors and keyboards all day.

In fact, experts say that watching these cute animals affects our brains' pleasure centers, releasing the same neurotransmitter -- dopamine -- that is also associated with substances like drugs and sugar.

Yes, that cute kitty playing with a ball of string might have the same effect as crack. Well, not quite, but almost. That's according to Oriana Aragon, a graduate student in psychology at Yale University who has been studying the effects of "cute" animals on the human psyche.

"Cute has a power over us," Aragon said. "We are drawn to cute things. That might be what you are tapping into when you are looking at animal webcams."

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Animal Planet recently partnered with the Washington Animal Rescue League, Audubon Nature Institute, the National Aquarium and the South Mountain Creamery to create a new site featuring animal webcam feeds. The network set up cams for kittens, puppies, penguins, ants, jellyfish, baby calves and tropical reef fish. Some creatures are obviously not as cute as others.

Researchers have known for years that we associate certain facial features with cuteness, whether in babies or kittens: wide set and large eyes, round features, a soft jaw, small chin and a big head-to-body ratio. Animal webcams attract viewers by showing the same ones.

Aragon likened the webcam to a place of relaxation, when the mind can take a break from the mandatory spreadsheet crunching or email writing that make up so much of our workdays.

"If you are using a lot of willpower to do your work, it could be that (watching an animal webcam) is a break," Aragon said. "Now you get to indulge this pleasantry without control."

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In a recent study, Aragon enlisted the help of 129 volunteers and found that those watching a slideshow of adorable animals popped more bubbles on a sheet of bubble wrap than did people viewing funny or neutral pictures.

This "cuteness aggression" didn't really mean that the subjects wanted to hurt the animals. Rather, Aragon and colleagues theorized that may be trying so hard to care for the cute animal that they displayed some inadvertent aggression (think a little girl trying to care for a cat so hard that she gets scratched).

The other theory is that the aggression comes from not being able to hold the animal on the screen, according to Aragon's study, presented at the January meeting of the Society for Personality and Social Psychology.

Aragon said she's curious which of webcams will be getting the largest number of followers: The network has set up cams for kittens, puppies, penguins, ants, jellyfish, baby calves and tropical reef fish. Some creatures are obviously not as cute as others.

Others have a more direct explanation for why people go goo-goo over live animal webcams.

"It's like a popularity of reality shows; these are animals doing what they do best, unscripted, fun, crazy, wacky stuff," said Bob Rimon, chief executive officer of the Washington Animal Rescue League. "It's cathartic to watch them. I feel like I'm going to shut my brain down and have pure fun."

At the San Diego Zoo, the live panda-cam can generate a million visits per month, crashing the server during births. The condor-cam is pretty popular, too.

"Maybe watching animal cams is a modern form of meditation," said Damien Lasater, design manager for San Diego Zoo Global. "Connecting to animals is often a healing experience and we have received numerous letters from viewers who have watched the cams to relieve stress."