This circuit -- constituted by a battery, a speaker, a nail, a piece of copper and wires -- gets connected whenever the nail touches the copper, and the flow of electrons would prompt the speaker to pulse. Since the copper is not perfectly even nor pure, the sound varies when the nail moves around the copper surface, as if playing a record. A contact mic was attached to the speaker to pick up the subtle noise. The speed and pressure of my engraving hand also affects the intensity and density of the clicking sound. The copper plate was later printed as dry point.