I've read somewhere that supersonic waves behave like supercritical flow of fluids and that subsonic waves behave similarly to that of subcritical flow. I guess an example of subcritical flow is pinching a hose and supercritical is how water flows over rocks (a bit more confused on that). Can you explain practical and possibly point me towards images how this is at all similar? I can see supercritical and supersonic but subcritical and subsonic is a bit harder. I guess since in the subcritical example, you are talking about faster wave propagation and it won't merge to become a big wave (I understand shockwaves may not work completely in this way). Thanks for answering.