The more I read about the devious indication of "bright frost" having "eternalized the bright eavesdrop" (the line itself seems so irrelevant & not only redundant), the more certain I am that it's a valid path to explore Nabokov's "style" and not some kind of mysterious addition.  

 

I understand that "stillicide" may not necessarily indicate a "frosty stalactite." Caves have other types of hardened sedimentation resultant from a mixture of dried- up water-drops and sand. Thomas Hardy himself didn't explicitly mention the term "eavesdropping" (ie, the formation of a stillicide and a gossipy "vine") - nor any ice !  Who uses both meanings (the drops from the eaves and its gossipy spirit) is Frost. And even there we have no clue about their being like Shade's "frozen stillicides" (Shade had to add the word "frozen", not true?)  

 

Frost's entire poem carries us to the moment when Shade reads to Sybil the lines in which he describes the night when his daughter died. Later we learn that Kinbote was noisily eavesdropping on them to hear the poem and he overturns the lid of a bin.

 

The actual day which Shade rendered in his poem includes the wind rattling a twig against a windowpane, an eery intrusion of an eavesdrop that is as  menacing as Goethe's Erlkönig ( CK  inteprets Goethe's Erlkönig as an "Alderking" and sees him as a homosexual, not Goethe, perhaps not Shade). It is another counterpoint to the moment Shade is reading about it. In the scene Shade describes then we find a first indication of Frost ( Shade being an oozy step behind him) and this scene, in turn, relates to Frost's lines about the murmuring couple's "inner haze."

 

Frost's poem was printed in an edition of Life-Magazine with his face on its cover.

 

A tricky matter: did Frost's poem appear before March 1962 (check attach with cover of Life-Magazine) and would Nabokov have had time to read and insert it in such an intricate pattern? It's rather doubtful. Pity. However, what a resounding "plexed artistry" seems to have taken place anyway!