You know a literary reference is obscure when you try to look it up online, and the only mention you can find takes you right back to the poem! Such was the case for Shmoop with words like "Hippocrene," a fountain of poetic inspiration. Chalk it up to Keats's amazing knowledge of Greek and Roman literature and mythology, which is up there with Shakespeare's (though Shakespeare is still the king in this department). Keats uses this knowledge oh-so-appropriately in a poem that derives from an Ancient Greek form, the ode. Show off.