dr. wolff likens his work to the way an intelligence service tracks threats made by potential terrorists. if he can track what viruses are crossing into humans, what he calls the viral chatter, he hopes to stop the next virus before it spreads. >> each one of the species of animals has their own sort of repertoire of different organisms. viruses, parasites, bacteria. and anytime that humans are in contact with those animals, there's going to be the possibility for the jump-overs. that's what we're considering the sort of chatter. the pinging, if you will, of viruses from these animals into the human population. and most of the times the ping just bounces back. but every once in a while, it sticks. >> it's sticking more often. the national academy of sciences says 75% of the world's emerging diseases jump over from animals. the sars virus crossed from civet cats in asia to infect thousands and kill more than 700 people in more than 20 countries. avian flu jumped over from birds around 2003 and k