A car’s indicator used to click because something inside it was getting hot. The old flasher held a strip of two metals bonded together: current warmed it, it bent until it broke the circuit, cooled, straightened, touched again, and each touch was a click, made louder by the metal can around it. Nobody designed the sound. It was the part working, overheard. In most new cars nothing moves at all; a computer switches the lamps in silence, and the click is a recording played through a speaker, because drivers who heard nothing assumed the indicator had stopped. For half a century the noise was an accident. Now it is the one thing in there made on purpose.