The overall tone of “The Flea” is dynamic and playful. The poem’s dynamism arises in part from Donne’s formal decision to alternate between lines of iambic tetrameter and iambic pentameter. This alternation between metrical forms produces a slight sense of being off-balance as the speaker attempts to convince his mistress to have sex with him. Her evident skepticism keeps her figuratively on a different rhythm, which forces him to find more inventive methods of persuasion. The speaker’s inventiveness is where the poem’s playfulness becomes most apparent. His outrageous conceit of the flea as a “marriage bed” (line 13) introduces us to his fertile imagination. Then, as his mistress resists his argument at every turn, he demonstrates the nimbleness required to change tack and improvise new arguments. Finally, the speaker brings a sense of playfulness through his introduction of numerous sexual puns. Consider, for instance, the moment when he counsels his mistress not to kill the flea, lest she kill him and herself as well (lines 16–18):

         Though use make you apt to kill me,
         Let not to that, self-murder added be,
         And sacrilege, three sins in killing three.

The references to “killing” here play on a common seventeenth-century pun that associates death with sexual intercourse. In this and other examples, the speaker showcases his playful and dynamic wit.