In addition to this primary compression wave, other waves, known as harmonics, are created. Harmonics are caused by factors including: the imperfect wobbling and shaking of the clarinet reed, the reed sealing the mouthpiece opening for part of the wave cycle (which creates a flattened section of the sound wave) and imperfections (bumps and holes) in the clarinet bore. A wide variety of compression waves are created, but only some (primarily the odd harmonics) are reinforced. These extra waves are what gives the clarinet its characteristic tone.