The essential feature of metaphysical poetry is its use of the conceit: an extended, elaborated metaphor in which two very unlike things, which hardly anyone would have thought to equate, are likened in a detailed, almost obsessive manner throughout a poem. As startling as such a comparison is at first, the poet finds one quality after another that both things have (or supposedly have) in common, laying out these points almost as we would the statements or proofs in a theorem.
In "The Flea," Donne likens the troublesome insect to the union of a man and a woman. In one of the most startling openings of any poem (I would argue) in the English language, the speaker tells the woman he's attempting to woo:
Mark but this flea, and mark in this,
How little that which thou deniest me is.
It sucked me first, and now sucks thee,
And in this flea our two bloods mingled be.
The mixing of the speaker's blood in the flea with the young lady's blood is a metaphor of the two having sex. This is the main...
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