A spile is a small wooden peg used to control the flow of carbon dioxide out of a cask of ale. Cask ale is served without externally-supplied carbon dioxide or nitrogen. The idea that it's served "flat" with no bubbles at all, though, is a misconception; properly conditioned cask ale contains bubbles of carbon dioxide generated by the natural action of the yeast living in the beer while it's transported and stored. In fact, the yeast will actually produce more carbon dioxide than is required, an… (More on Spile)