The Puppeteer puts it right at the back of their mouth so that when they speak, a little reed or something inside it resontes to produce the distinctive Mr Punch voice. The downside is that all other voices must be done whist it is still in place meaning that quite a few have been accidently swallowed. In the UK, you arent considered a Punch and Judy Professor unless you have swallowed your swazzle at least twice.