Analysis of Dying (I heard a fly buzz when I died)

I heard a fly buzz when I died;
   The stillness round my form
   Was like the stillness in the air
   Between the heaves of storm.
   The eyes beside had wrung them dry,
   And breaths were gathering sure
   For that last onset, when the king
   Be witnessed in his power.
   I willed my keepsakes, signed away
  What portion of me I
  Could make assignable, -- and then
  There interposed a fly,

With blue, uncertain, stumbling buzz,
  Between the light and me;
  And then the windows failed, and then
  I could not see to see.