The image of the bog completes the frog metaphor introduced two lines prior. By characterizing the public audience as “an admiring bog,” the speaker devalues it. A bog, after all, is a section of spongy land, full of stagnant water and decaying matter. The idea is that any attempts at self-aggrandisement or posterity one might throw to the world will end up in a bog—going nowhere, rotting.
