What metaphors are used in Porphyria's Lover by Robert Browning?

In the second half of the poem, Browning offers more and more clues to show that the speaker is not merely delusional or confused because of his near-broken heart but that he is quite mad. Yet all this is presented, again, in a manner of eerie calm, even as the speaker describes how he takes his lover's hair and twists it around her neck until she is dead. At the moment of her death, there is no shift in rhythm (although the language of the poem does become progressively more metaphorical throughout the poem), and the detachment with which her death is reported makes the scene all the more shocking. At the end of the poem, it is obvious that the speaker has completely lost touch with reality, but again neither the tone nor the diction points overtly to his madness. Rather, the reader gets a sense of his dementia from what the speaker does not say, from how his depiction of events cannot possibly accord with reality, and from the incongruity of his insistence of his lover's happiness with the fact that she lies dead in his arms.