Vibrations of the strings of musical instruments are far more complicated than is commonly assumed. On such a string, a large number of higher harmonics of different amplitudes are usually superimposed (which may explain the difficulties for musicians to play a string instrument well). This complexity is also observable in the motion of sections of the string, as will be shown in this experiment. A violin string is stretched perpendicularly across an optical bench, and can be excited either by plucking, or by striking it with a bow. An arbitrary spot of the string is illuminated through a vertical slit, and is projected on the wall of the lecture hall. The string is plucked, as can be heard. The slit with the vibrating section of the string is shown on the projection screen. As the disk with the lenses is rotated, the time-dependent motion of the section is displayed. It is by no means a simple sinusoidal oscillation. Rather, the pictures show amazingly complicated patterns. Similar patterns are also obtained with a stroked string.