How does the author use metaphor in the story, To Da-duh in Memoriam?

The planes that Britain sends over the island do not look or act like objects of the machine age, but like "swooping and screaming . . . monstrous birds" or "the hardback beetles which hurled themselves with suicidal force against the walls of the house at night"; this use of metaphor shows that despite hearing about New York and the modern world, Da-duh cannot even fathom its existence.