A lionfish is a swimming paradox. It is painted in fierce hues of orange and white but it has an almost melancholy expression. It has fearsome venomous spines sticking out of its back, but elegant fan-shaped fins protruding from its side. And although it floats with an indolent air, it is actually an active and skilled predator—one that hunts in teams using surprisingly sophisticated tactics.

That’s how the hunts end. But Lönnstedt was more interested in how they start.

She noticed that they always begin when one lionfish swims up to another, points downwards, flares its pectoral fins, and quickly undulates its tail. After a few seconds of this, it slowly waves one pectoral fin, then the other. The partner almost