The terrain is rough, autumn in New England, orange leaves thick on a steep hill. The creature struggles with a heavy pack, all four legs straining away, making its way upward, threading through the trees. At the plateau, someone gives it a swift kick in the side and it tumbles sideways, staggering, pivoting, compensating for the blow, one leg crossing back across the other, balletic, elegant. Balanced again, the creature would, to assess its surroundings, hold its head up — if it had a head. Instead there’s just a space where that should be, because the creature is a “BigDog” robot, symmetrical in either direction, designed to mimic the motion, balance and fluidity of an animal with the relentlessness of a machine.