In Chaucer's The Canterbury Tales, the author uses "The Nun's Priest's Tale" to show how the world of human behavior overlaps with that of animals.
The story related uses animals; it is a moralistic tale—there is a lesson to be learned, but the storyteller uses less sermonizing and more tale-telling to get his point across without sounding "preachy."
The human side of the animals is seen with Chanticleer, the rooster. He is owned by a poor widow—a woman who struggles to run a farm with her children. She is a good person who works hard, whle caring also for two daughters and farm.
Chanticleer is admired for his wonderful voice; he has a bevy of hens (his "wives"). Like a man, his "sin" is pride and arrogance. It is this shortcoming that leads Chanticleer to his near demise because he gives in to flattery, but he is also redeemable—learning his lesson saves his life.
The fox is portrayed as clever and deadly (seen in many stories that include the character of a fox). He wants Chanticleer for breakfast. He uses Chanticleer's pride to lure him away, flattering him. His sin is deception.
[The fox represents] the beast who acts like a man...
In the story, the animals are given human characteristics to teach a moral lesson.
...beasts personify humans and exaggerate Man's characteristics, usually for the purpose of teaching a lesson...
And so, when the fox flatters Chanticleer and asks him to crow, the bird opens his beak and stretches his neck. The fox grabs the bird and takes off. Meanwhile, the hens screech in protest, which draws out the wife and her children. They, along with the other farm animals, pursue the fox.
Chanticleer is no slouch either. Having learned his lesson, he uses the fox's same tactic to trick him into dropping his quarry. He convinces the fox to tell his pursuers to leave him alone as he is so fast that they will never catch him. Chanticleer's flattery works and the fox gives in to his own pride: he starts to speak, and Chanticleer flies into a tree. Though the fox tries again to lure him back, the rooster knows better.
The "beast" of Chanticleer exhibits human frailties such as pride. The fox demonstrates a dark side of the humanity in practicing deceit and manipulation. The other animals represent righteous folk who drop everything to come help a neighbor and/or friend in dire need. "Beasts" are used to represent human beings.
The story's message is clear: avoid giving in to flattery.