"whose back was higher than his head, whose lopsided mouth said Grazie in a voice as sweet as a child's when she speaks to her mother or a bird's when it spoke to St Francis."
By his use of the climactic list as well as the anaphora - 'who', 'whose', 'whose', - the speaker contrasts the sheer suffering and ugly appearance of the dwarf, whose 'eyes/wept pus', whose 'back is higher than his head', and who has a 'lopsided mouth'. The speaker uses contrast, along with the use of the list and anaphora, to compare once again the physical ugliness and disgusting appearance of the dwarf to St Francis in the first verse and to the child in the lines that follow.
The speaker uses the list of the dwarf's repulsive features to stress how hideous he looks as well as anaphora of the relative pronoun 'whose' (making clear to whom these features belong). The use of enjambment then forces 'said Grazie in a voice as sweet' onto the next time, drawing attention to the way the dwarf's outward appearance contrasts with his kindness, politeness, and inner beauty.
The comparison with a child evokes our sympathy and makes us aware of his anguish and helplessness. The final two lines refer back to St Francis, who was so kind that birds spoke to him.