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SAN FRANCISCO, CA - DECEMBER 03: A young girl pets a therapy dog named Donner inside Terminal 2 at San Francisco International Airport on December 3, 2013 in San Francisco, California. The San Francisco SPCA and San Francisco International Airport joined forces to launch a new program called "Wag Brigade" that will have a team of certified therapy dogs that will patrol the airport's to help calm stressed travelers during the busy holiday travel season. (Photo by Justin Sullivan/Getty Images)

SAN FRANCISCO, CA - DECEMBER 03:  A young girl pets a therapy dog named Donner inside Terminal 2 at San Francisco International Airport on December 3, 2013 in San Francisco, California.  The San Francisco SPCA and San Francisco International Airport joined forces to launch a new program called "Wag Brigade" that will have a team of certified therapy dogs that will patrol the airport's to help calm stressed travelers during the busy holiday travel season.  (Photo by Justin Sullivan/Getty Images)