A buckled beam stores elastic energy on both sides of its snap-through point. Push it past the threshold and it snaps to the other side, releasing the stored energy all at once. The beam is bistable, and the snap is violent — useful for latches, switches, and bistable mechanisms. But the beam doesn’t snap on its own. It needs an external push.

Non-reciprocal interactions change this. When the coupling between the beam’s internal degrees of freedom is asymmetric — when the response to being pushed doesn’t equal the capacity to push back — the beam passes through an exceptional point and begins to self-oscillate. It snaps back and forth without external input, converting the asymmetry of its internal coupling into autonomous motion.

The surprise is the multiplicity of functions this enables. A single active filament, powered only by its non-reciprocal buckling dynamics, can crawl along a surface, dig into a substrate, or walk with alternating contacts. Three qualitatively different locomotion modes from one mechanism, selected by boundary conditions rather than by redesigning the beam.

The filament doesn’t need a controller to switch modes. It doesn’t need actuators or sensors. The locomotion emerges from the interaction between the non-reciprocal instability and the environment — the same self-snapping beam crawls on a flat surface and digs into a soft one, without any change to its internal parameters.

One instability, many functions. The mechanism is the material; the environment selects the behavior.