This story is not about the pros and cons of gravy. The point is that sometimes we can be familiar with something we really enjoy, but have no idea what it actually is. This is the relationship most of us have with music – pleasure without understanding. To my shame, I must admit that I still don’t know what goes into gravy, but I have managed to untangle some of the ingredients of music, and I hope you enjoy my explanation of how musicians manage to manipulate our moods using only string, bits of wood and lengths of tubing.