This is what your Harmonix harmonica looks like inside. It comprises a cartridge, which holds the reeds and is the part that makes the sound, a housing which holds it all together and a rear module that can be a dummy (BX1), a recording module (EX1) or a stage work module (WX1). The harmonica makes sound by passing air over brass reeds, which vibrate in slots. The reeds and their slots vary in length so achieving different notes.

The air passing over the reeds is made by you when you either BLOW or DRAW, (`DRAW` is just another word for suck).