Unda is the Latin word for wave. It is interspersed with the proof-reader's sign which means 'transpose the two facing letters', which in this context becomes also 'the sign of the wave'. The signs are so placed that they move from right to left, in opposition to the normal left to right direction of the letters: an ebb and flow is therefore created in the poem. As it advances, the sign transposes the letters in a formal imitation of the spinning movement of waves. UNDA emerges at the end of this process in a clear, and pure, state.