The poem The Flea by John Donne uses a surprising and potentially gross extended metaphor to compare the speaker and his mistress to a flea that has bitten them both. The speaker argues that their blood is already mingled inside the flea, so having sex would not be a sin or a shame. He also compares the flea to their marriage bed and temple, implying that they are already united in a sacred way. He even invokes the Holy Trinity to persuade his mistress not to kill the flea, which he says would be a triple sin of self-murder, murder, and sacrilege. The poem is full of unexpected comparisons that challenge the conventional views of love, lust, and religion in the Renaissance period. Some of the comparisons are:

• This is a metaphysical poem in the sense that it uses a complex and original conceit, or a comparison between two very different things, to explore a philosophical topic. The topic is the nature of love and its relation to physical and spiritual realms. The conceit is the flea that has bitten both the speaker and his beloved, and that represents their union and marriage. The poem also uses paradoxes, such as “marriage hearse” and “three lives in one flea spare”, to create a contrast between the conventional and the unconventional views of love. The poem also uses religious imagery, such as the Holy Trinity and the sacrilege, to challenge the authority of the church and to elevate the status of their love. The poem is a typical example of metaphysical poetry, a genre that was popular in the seventeenth century and that was marked by bold and ingenious conceits, incongruous imagery, complexity and subtlety of thought, frequent use of paradox, and often by deliberate harshness or rigidity of expression