From lobster claws and dog teeth to bee stings and snake fangs, every creature depends on a weapon. But some are armed to extremes that make no practical sense—whether it's bull elks with giant 40-pound antler racks or tiny rhinoceros beetles with horns bigger than their body. What explains giant tusks, horns, and claws that can slow an animal down and even impair health and nutrition? NOVA investigates the riddle of outsize weaponry and uncovers a bold new theory about what triggers an animal arms race. In creatures as varied as dung beetles and saber-toothed tigers or shrimp and elephants, the same hidden factors trigger the race and, once started, these arms races unfold in exactly the same pattern. Join scientists as they crack the secret biological code that underlies nature's battleground.