What really defines the harmonica is its sound and style that can be produced. This Ten-Holed Tin-can Tongue Twister is based on the diatonic scale, Do–Re–Mi–Fa–Sol–La–Si–Do. Within each hole of the diatonic harmonica there are multiple of notes that can be played by either drawing air or blowing air into the harmonica. “The most common diatonic harmonica is in the key of C major, with the blow reeds producing the C, E, and G notes of a C chord and the draw reeds producing the D, B, F and A notes.” (E-how) Yet the basic blowing and drawing will only get you two notes, to unlock the different pitches, one must learn how some “mouth voodoo” (Harmonica 101), commonly known as note bending.
Advanced players know that the shape of the throat, the movement of the tongue, and the pressure and angle at which breathe is applied all influence the quality of the notes. Furthermore, skilled harmonica players can achieve non-diatonic notes even on a diatonic harp by producing what are called overblow bends (E-How).