LOS ANGELES - When Shetland sheepdog Maggie comes home from the groomer, her owners praise her shiny coat, much to the chagrin of pit bull Stormy, who will head-butt her until their family cuts out the compliments.

After hearing stories like these, a psychology professor studied if the human emotion of jealousy happens in dogs. The nine-month study published in PLOS ONE hints that it could be possible, but other experts aren't so sure the behavior can be called jealousy.

"While I will not say that dogs do not experience jealousy, this article does not prove that they actually do," said Dr. Bonnie Beaver, executive director of the American College of Veterinary Behaviorists and a professor at Texas A&M University's College of Veterinary Medicine.

But Christine Harris, a professor of psychology at the University of California, San Diego, says her dog study supports the theory that there's a more basic form of jealousy. She and a former student worked with 36 dogs, videotaping owners ignoring their pets while petting and talking to stuffed, animated dogs or jack-o-lantern pails.