A swazzle -- AKA a swozzle, schwazzle, swatchel, or squawker -- is a sort of mini-kazoo for making silly voices. It is made of two flat strips of metal or other stiff material bound together with a small reed between them. The reed is usually made of a bit of cotton cloth, such as twill tape.
The swazzle is traditionally used to give puppets squeaky, buzzy, distorted voices, and is most famously used in Punch and Judy shows. While sounding quite a bit like a kazoo, the swazzles are small enough to be held entirely within one's mouth, allowing for a better approximation of human speech... although it certainly remains an impediment.
The puppeteer -- in Punch and Judy shows he is officially titled The Professor -- holds the swazzle between the blade of the tongue and the roof of the mouth, shifting it within his mouth to switch voices between the swazzled speech and more normal tones. Due to the dexterity required, it is apparently necessary to have a string tied around the swazzle to rescue it in case The Professor swallows it by accident.