The MLP in the last lesson knew nothing about the world. Here is what it was missing. Any rigid mechanical system — a pendulum, an arm, a humanoid — obeys one equation: M(q)q̈ + C(q,q̇)q̇ + G(q) = τ. M(q) is the mass/inertia matrix (how hard each joint is to accelerate, and how joints are coupled); C(q,q̇)q̇ are the Coriolis/centrifugal terms; G(q) is gravity; τ is the applied torque. The Bench integrates a real double pendulum with ferromotion-core: every frame it builds M(q), the gravity bias, and solves M q̈ = τ − bias. Watch it swing (chaotically — this is the famous double pendulum), and watch M(q) and G(q) change as the configuration changes. That dependence on q — the coupling, the geometry — is knowledge no amount of data teaches a black box for free.