Threshed corn lay piled like grit of ivory
Or solid as cement in two-lugged sacks.
The musky dark hoarded an armoury
Of farmyard implements, harness, plough-socks.
The floor was mouse-grey, smooth, chilly concrete.
There were no windows, just two narrow shafts
Of gilded motes, crossing, from air-holes slit
High in each gable. The one door meant no draughts
All summer when the zinc burned like an oven.
A scythe's edge, a clean spade, a pitchfork's prongs:
Slowly bright objects formed when you went in.
Then you felt cobwebs clogging up your lungs
And scuttled fast into the sunlit yard-
And into nights when bats were on the wing
Over the rafters of sleep, where bright eyes stared
From piles of grain in corners, fierce, unblinking.
The end of stanza three is  enjambed  with stanza four, expressing the speed and fear of the child. The verb ‘scuttled’ is vivid, suggesting nerves and a rapid, scrambling movement. 
 The dash after ‘yard’ forms a  caesura , a pause, to change the mood again.
The Barn