Guest who doesn't believe Barry Finn, - Extemporare verses are quite common in work songs. In the Gaelic waulking song tradition, that though many songs have "standard" verses, many of the singers would add verses to tie local people and events into the song, usually to poke fun at younger women and men, sometimes to warn a woman about a man or to encourage the pairing in other instances. These people who do this are trained to do this. Perhaps you and I couldn't do it, but people who know the rhythm of the song and the people involved could create such verses on the fly with ease. I've seen it done. I know it is possible. For instance, Nelson's Blood is one where it's so short singers will often add to it. Please don't scoff, it can and does happen.