"He walked the ribbed sand under the flat keels of whales,
under the translucent belly of the snaking current,
the tiny shadows of tankers passed over him like snails
as he breathed water, a walking fish in its element."
He mixes the language of the land and the language of the sea to paint a picture of what it would be like for a man to stand on the ocean floor. I suppose the mixing of two worlds is something he is very familiar with.