Round characters, characters who are fully developed, have many sides to their personalities, so much so that they are often perceived by readers as realistic. The Nun's Priest's tale is much like a fable as the rooster, the hen, and the fox are anthropomorphized, or given human qualities, and the tale leads to a moral lesson.
Chanticleer, the rooster, is a vain male that has several hens, the favorite of which is "the winsome Pertelot." One day
This Chanticleer he groaned within his throat
Like man that in his dreams is troubled sore.
Pertelot asks what is troubling him, and he replies,
I pray you that you take it not in grief,
By God. I dreamed I’d come to such mischief....
And, he tells his love about a beast that kills him. Pertelot scolds him for not being a man, though he has "a beard." In reply to her, Chanticleer relates the story of a man who had a similar dream and was, in fact, killed. But, foolishly he listens to Pertelot--"took the counsel of his wife, with sorrow"--and does not heed his dream. Later, however, a fox slyly watches the chickens, and tells Chanticleer that he means no harm and only wishes to hear him sing. Thus deceived by this flattery, Chanticleer, like his father, closes his eyes to crow, and the fox grabs him by his throat and carries him off. But, the quick-witted Chanticleer, realizing his foolishness, plays upon the pride of the fox and tells him to turn and taunt Mistress Pertelot and the others who pursue him by saying,
"‘Turn back again, presumptuous peasants all!
A very pestilence upon you fall!
Now that I’ve gained here to this dark wood’s side,
In spite of you this cock shall here abide.
I’ll eat him, by my faith, and that anon!’”
The gullible fox does just this, and when he opens his mouth, Chanticleer jumps out and flies upon a branch in a tree. Then the fox tries to trick the rooster, but the wiser Chanticleer tells him,
If you beguile me, having done so once,
You shall no more, with any flattery....
Clearly, then, Chanticleer is a round character; for, he has learned and developed from his earlier mistakes of letting flattery from Perteloe convince him to disregard his dream as well as the cajolery of the fox to get his to close his eyes as he sings. Wiser now, Chanticleer will not be fooled a third time.