Rann

from J. Campbell and H.M. Robinson, A Skeleton Key to Finnegans Wake:
"A rann is an ancient Celtic verse form. There are many stories of Irish poets who revenged themselves against ungenerous or brutal kings by composing satires against them..."
"'The wren, the wren, the king of all birds, St. Stephen's day was caught in the furze'. A traditional song sung on St. Stephen's day, when a wren is killed and carried about the town on a stick."