text:  Most animal viruses, like the first SARS-1 back in 2003, it didn't transmit very well. So it could get into humans, and it was pretty deadly, about 10% deadly. But it didn't transmit very well. So if people just stayed home when they were sick, it sort of burned itself out pretty quickly. But mutating is the biggest danger. The biggest danger for avian flu or, frankly, for Spanish flu. The Spanish flu was from 1918, and somewhere between 50 and 100 million people died worldwide.