Between my finger and my thumb
The squat pen rests; snug as a gun.
Under my window a clean rasping sound
When the spade sinks into gravelly ground:
Heaney begins, characteristically, with a direct opening, without preamble, to draw the reader in. The  imagery of ‘finger and thumb’ is powerful, however, bringing to mind the act of holding a pen and writing — something positive.  It also refers to the action of shooting, with the thumb readying the weapon and the forefinger pressing the trigger.  The latter is, of course, ironic. This is an oblique reference to The Troubles' in Northern Ireland. 

Digging