In John Donne’s poem “The Flea,” the blood represents the physical union between the speaker and his lover. The flea has bitten both the speaker and his lover, and as a result, their blood has mingled inside the flea’s body. The speaker uses this as a metaphor for their shared experience of physical intimacy, suggesting that they have already experienced a kind of union through the mingling of their blood inside the flea.
The blood symbolizes the physical aspect of their relationship, and the speaker uses it to try to persuade his lover to have sex with him. He argues that since their blood has already been mixed inside the flea, they have already experienced a kind of union, and there is no reason for her to resist him. Overall, the blood symbolizes the physical connection between the two lovers, and serves as a means of persuasion for the speaker in his attempts to convince his lover to sleep with him.