http://news.yahoo.com/s/ap/20051212/ap_on_fe_st/dog_laughter_1
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Woof, woof, grrrrrr!
SPOKANE, Wash. - An animal behaviorist says she's figured out what dogs are doing when they make that excited panting noise while playing or anticipating a much desired walk. They're laughing.
Patricia Simonet, development and program coordinator for Spokane County Regional Animal Protection Service, also found that the sound of dog laughter comforts other dogs. When she played a recording of "play panting" through the speaker system at a shelter in Spokane Valley, all the barking dogs quieted within a minute.
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Woof, woof, grrrrrr!