This is the story of the great Gaelic hero Fionn MacCool and why he sucks his thumb. It is also the story of the Salmon of Wisdom on the Gaelic flag of Nova Scotia. The tale is retold as a participation story, combining gestures and action words to introduce children to the Gaelic oral tradition of Nova Scotia, Scotland, and Ireland. A version of the tale in the Scottish Gaelic language is included at the end of the book.