The material, leather, mutes the distinctive character of the instrument's tonal qualities less than other materials. The player is better able to hear the ringing of the overtones under the ear, resulting in improved intonation and a more "vibrant and glorious" sound.
You can customize the fit of your mute. Moisten the two small notches with a drop of water, an the place the mute back on the strings. During the drying process, the notches will reshape and conform to the string dimensions of you instrument.