Teeth pass through each other
The animation spins the planets on their pins. In physics those pins are locked and the centres sit too close, so the teeth overlap (red).
Comparison demo
An animation always plays.
Animated mechanisms have no mass and no contact, so nothing ever stops a part. We replay the same parts in physics.
A stool that cannot fold
The animation folds the X frame. In physics each foot is a slider that cannot tilt, so the frame stays open.
Ours: it moves in physics too
Under the same small push our wiper sweeps in physics. The arm stops at its designed limit, which the animation swings past.
Animated toys are primitive parts moved by closed-form kinematics, the way animation-based methods present mechanisms. Physics runs the same parts with mass and contact under a small push on one joint. Red marks triangles that intersect another part.