An outbreak of pneumonia in central China is causing alarm. The reason? Doctors have ruled out all known causes of respiratory diseases, meaning the pathogen is a mystery. One potential clue: Some of the patients worked at a seafood market where birds, snakes, and organs of rabbits and other game were also reportedly sold. That’s heightened concern that the disease might have come from animals — reminiscent of the novel virus that sparked an epidemic of Severe Acute Respiratory Syndrome, or SAR