This is the story of the great Gaelic hero Fionn MacCool and why he sucks his thumb. This traditional Gaelic tale is retold as an action story to read aloud. It introduces children to storytelling and to Gaelic oral tradition, language, culture, and belief systems. The action story presents gestures corresponding to nine keywords in the story. As the story is read aloud, children perform the matching gesture whenever they hear each keyword. The book contains two versions of the action story, the first entirely in English, and the second in English with Scottish Gaelic keywords. Once children become familiar with the all-English version, the second version with Gaelic action words can be introduced. The actions are the same in both versions, and act as a bridge to introduce the Gaelic vocabulary and increase awareness of the language. This story is one of the tales of the boyhood deeds of Fionn MacCool (or Fionn MacCumhail as he is known in Gaelic). The tale is rooted in the oral traditions of pre-Christian Celtic culture, and the earliest known written version dates to the 12th century CE. Tales of Fionn and his band of Fiana were popular across the Gaelic world, from Ireland to the Isle of Man and Scotland. Scottish Gaels brought tales of Fionn MacCool to Nova Scotia beginning in the 18th or 19th century and transmitted them orally from one generation to the next as part of their Gaelic culture. Fionn tales were recorded in Nova Scotia in the 1970s and form an important part of Canadian Gaelic heritage and culture. The book is suitable for reading aloud at Gaelic and Celtic cultural events, in community group activities, and in schools as a part of lessons on Gaelic culture, English language arts, public speaking, theatre or drama studies, geography, history, and child studies programs. Adults, teens, and older children can read the story aloud to a group, or adapt the story in various ways as the centrepiece of a lesson on Gaelic culture and beliefs. A link to a free teaching guide with pronunciation videos is included in the introduction.