A beginner on the guitar may play the wrong note, but the single note will still be recognizably ‘musical’, but a first attempt to bow a violin string, it is only too easy to make a truly dreadful noise on it. This contrast points to the most basic difference in physics of plucking a string versus bowing one: the plucked string is almost a linear system but a bowed string is strongly nonlinear. Plucking a string elicits a mixture of its natural frequencies, which are nearly harmonically spaced. Bowing elicits a self-sustained oscillation through the slip-stick action of friction between the bow-hair and the string.