For the past few years, orcas off the coast of Portugal and Spain have been attacking, and sinking, small boats. At least three boats have been completely sunk, and many more have needed urgent rescue. This behaviour doesn't occur in other orcas, and nobody can figure out exactly what's changed.There are some theories regarding trauma, or differences in their habitat. There are very real things called "orca fads"—like that time they wore dead salmon on their heads. And there is, always, humanity's endless desire to use our own narratives to explain animal motives—which is why you see people asking if the orcas are fighting back. But what's really at the heart of this behaviour? And what happens if it spreads?GUEST: Stephanie Pappas, science journalist, writing in Scientific American