Metaphor in Ode on a Grecian Urn

Text of the Poem 1
"a parching tongue..."   (Text of the Poem)

Keats compares the effects of "breathing" or mortal passions with a disease whose symptoms include fever ("a burning forehead"), dehydration ("a parching tongue"), and a broken heart. The word "cloy'd" also suggests that human passion is sappy or overly sweet, where the immortal love on the urn is timeless and refined.