the descent of parachuting words onto the sands of the page; (4)
How would this line be different if it were about words as fighter pilots instead of parachutists?
the beheading of epithets, the burial of mirrors; (8)
The violence of beheading and burial in this line shows just how cleanly poetry cuts off (rim shot, please!) language from what it is talking about. The use of symbols and metaphors is not direct language, but rather an indirect version that illustrates rather than replicates reality.
the recollection of pronouns freshly cut in the garden of Epicurus, and the garden of Netzahualcoyotl; (9)
There's that cutting again! Just like the epithets got their heads cut off in line 8, here the pronouns are being lopped off like blooms in a garden. Figurative, or poetic, language is separate—cut off—from reality.