John Donne attempts to convince his girlfriend to give up her virginity to him in "The Flea." In this poem, the speaker notices that a flea has bitten both him and his would-be lover. He then goes on to use the presence of the flea to validate his seduction. The flea has bitten both of them, and according to the speaker, the mingling of the blood in the flea has already consummated their bond.
Donne uses the flea as a metaphor in these lines twelve and thirteen:
"This flea is you and I, and this
Our marriage bed, and marriage temple is."
Using this logic, Donne makes his case that the flea has already joined them, so his lover should also yield.