"Seinn O" comes from the Gaelic tradition of “mouth music,” a style of vocal music intended to accompany dancing. The most popular legend of the origins of Scottish mouth music (port a beul) suggests that it was born when the British banned the bagpipes after the Jacobite uprising in 1745. Nonsense lyrics were applied to the old pipe tunes so that the precious melodies wouldn’t be lost. Whatever the truth of the matter, mouth music appears in many varied forms and under many names in every Gaelic culture in the world, from Ireland to Cape Breton to Appalachia.
Like most mouth music, the lyrics are light, flirtatious, and improvisatory, with a healthy amount of nonsense. The speed of the music, the call-and-response structure, and the inconsequential nature of the lyrics makes the song seem like a party game or a bar bet to see who can trip up the tongues of their opponents.