do madmen shake your memory?

A curious thing, following my train of thought on 'Rhapsody on a Windy Night' by T.S. Eliot after Lara's comment the other day. 'Rhapsody' is probably my favourite of Eliot's poems and predominantly because of the pair of lines,

Midnight shakes the memory
As a madman shakes a dead geranium.

They are, in fact, the inspiration for the title of my interminably in-production novel, as well as forming its epigraph. And, in the process of pondering how exactly a madman does shake a geranium and what that says about midnight and its effect on the memory, I came across this, from Robert Scruton's The Aesthetics of Music.

The surface grammar of a simile may belie a metaphorical intention, as when Eliot writes:

Midnight shakes the memory
As a madman shakes a dead geranium.
('Rhaspody on a Windy Night, in Prufrock, and Other Observations)

Midnight does not literally shake, nor is the memory literally shaken; the comparison implied by 'as' assumes a prior metaphorical transfer. And even so, it cannot be carried through. Midnight is not like a madman, nor memory like a dead geranium. Nor do the llines imply the contrary; rather, they bring the image of a madman shaking a dead geranium into proximity with the poet at midnight, helplessly and uselessly 'remembering thing'. The result is not a comparison but a highly imaginative fusion, of the kind we know from metaphor.

Which I think solves... some of the puzzle of the image for me. I understand what Eliot means but the... practicality of the image has always thrown me slightly and now I know why.

(For those unfamiliar with Eliot, here's a copy of all of Prufrock, and Other Observations.)