A magnet is not uniformly magnetised — it breaks into domains to shed its own field, separated by Bloch walls where the spins rotate through. Magnetise it and the walls jump between pinning sites in discrete clicks, which is the Barkhausen noise you can hear; every hit moves a wall.
Drawn with: a WebGL2 shader.
Reacts to and looks like: gpu, webgl2 and audio-reactive.
Family: Visualiser.
Runs in your browser. The preview above is the same program the renderer uses.