I slipped my feet into them as if into jewel cases woven with threads of dusk and sheep's wool. (8-16)
The socks, in this first instance of slipping onto the speaker's feet, undergo their first transformation from being an ordinary object to jewel cases, somehow magically made out of dusk. The elevation of the everyday begins here.
Audacious socks, my feet became two woolen fish, (17-20)
Once the socks have transformed, they then transform their contents: the speaker's feet. The magic of poetic transformation is contagious.
two long sharks of lapis blue shot with a golden thread, (21-24)
Now it looks like the socks and the feet are melding into one—the feet become sharks that are shot with golden thread.
two mammoth blackbirds, two cannons, (25-26)
Now the transformations come faster and faster, one per line as the feet become blackbirds, then cannons. The speaker, it seems, is inspired by the beauty of the socks to rap off a list of images. In this way the socks transform not only themselves and the feet, but the speaker's perspective as well.