There is no pun. This poem is genius. Ashbery's whole thing is that he doesn't always have to make sense, that he's allowed to make sense. He's called post modern b/c his poetic functions like this, b/c he contrasts images for the sake of the contrast, b/c new relations create new possibilities. Often his poems work like a photo album of unrelated images, with one final line to draw it all together "life it's marvelous / follows and falls behind" etc. This poem is what it is. There's nothign more than that. It's funny. It's fairly clever. It's ashbeyr.