Shelter Cat

It might have been her eyes, or the way he moseyed up to the front of his cage. The reasons differ, but many pet parents will tell you they immediately knew that their shelter animal was "the one."

A new study by the ASPCA aims to decode the science behind how and why people pick the pets they do. From January through May of last year, about 1,500 adopters at five shelters filled out questionnaires about selecting their pet from the shelter. Respondents were able to rank multiple reasons, like age, behavior and physical appearance.

The study found that for both adult dogs and cats, behavior with people was the most important category for potential owners, with age as the least important. Those interested in kittens, however, ranked age as most important, while potential puppy parents were most focused on physical appearance. Interestingly, physical appearance was least important to those shopping for kittens, while behavior with people ranked last among those looking for a puppy.

"That's a clue to shelters that they might want to have a conversation with adopters to help them see past the skin-deep beauty, and to the inner beauty of an animal, so they can form a lifelong commitment, a little bit more than a skin-deep commitment," the ASPCA's Dr. Katherine Miller told the Wall Street Journal.

Watch the Wall Street Journal's interview with Dr. Katherine Miller, and tell us: How did you know your shelter pet was "the one?"