From, "Same Old Man, Sittin' At The Mill" (that other thread) this verse. It's not Celtic, nor is it the subject of the song, but it's a great verse....
Purty little leaf, lying on the ground,
Now you're turning slightly brown,
Why don't you hop back up on the tree,
Turn the color green the way you oughta be.
For more H.M.R. with a trivia question, see the thread about dirty lyrics to folk songs.