We tend to think of the flu as something seasonal — a nuisance we can fend off with a shot and a bit of luck. But what if the real threat isn’t just circulating among humans… but quietly evolving in birds?

Today’s guest has spent his career at the frontlines of that invisible border — the place where animal viruses spill over into people. Dr. Richard Webby is a virologist at St. Jude Children’s Research Hospital in Memphis, Tennessee, and he studies the influenza viruses most of us rarely think about: the ones still living in aquatic birds, waiting for their chance to jump.

In our conversation, he walks us through the intricate, often surprising world of influenza A — including the H5N1 virus making headlines today — and how scientists like him are racing to understand which strains could pose the next big threat.