Nothing is done, nothing is said,
But don't make the mistake of believing us dead:
I shouldn't dance.
We're afraid in that case you'll have a fall.
We've been watching you over the garden wall
For hours.
The sky is darkening like a stain,
Something is going to fall like rain
And it won't be flowers.
When the green field comes off like a lid
Revealing what was much better hid:
Unpleasant.
And look, behind you without a sound
The woods have come up and are standing round
In deadly crescent.
The bolt is sliding in its groove,
Outside the window is the black remov-
Ers' van.
Echoes the scene in Act V of Shakespeare’s  Macbeth  in which soldiers shielded with branches from Great Birnam Wood advance on Dunsinane Hill, fulfilling the three witches' prophecy that Macbeth will be safe until Birnam Wood has come to Dunsinane. Like most of the images of the poem, this one spells impending doom. 
 Much as the three witches or “Weird Sisters” in  Macbeth  seem to be agents of fate (modeled on the three Fates from Greek mythology), “The Two” in this poem speak as ominous, voyeuristic, possibly supernatural presences with some knowledge of and control over our destinies.
The Two