The fact that this is grammatically isolated adds a melancholic tune to the poem, and also in parentheses. This heightens the multi-sensory concept, (seen in the first stanza) the sense of which the poem embodies, of longing, being a mechanism to impose the feeling of nostalgia upon the reader. Perhaps Duffy here wants us to sympathise with the lives of the mercenaries, which could make us recognise their tough job. It could also make the readers imagine a sad, soft song playing in the background, which could reflect how the mercenaries' lives were desolated.