The Brodies predicted that if snakes and newts are coevolving, their traits should match up — that is, because TTX production is costly for newts and TTX resistance is costly for snakes, newts should be just toxic enough to avoid predation and snakes should be just resistant enough to eat a newt. Coevolving organisms often match traits this way.
When the Brodies and student Ben Ridenhour compared snake resistance and newt toxicity in different populations of snakes and newts they found just what they predicted: a close match. Where low toxicity newts occur, the snakes in the area have low resistance. Newts of intermediate toxicity occur with snakes of intermediate resistance, and in some populations, the Brodies discovered extremely toxic newts that were being eaten by snakes with extreme resistance.