> When an instability is detected while walking and the robot stabilizes after pumping energy into the system all is good, as that excess energy is taken out of the system by counter movements of the legs pushing against the ground over the next few hundred milliseconds. But if the robot happens to fall, the legs have a lot of free kinetic energy, rapidly accelerating them, often in free space. If there is anything in the way it gets a really solid whack of metal against it. And if that anything happens to be a living creature it will often be injured, perhaps severely.