Alisoun, John's wife, Nicholas's lover, and a reputed local beauty, is the only character in "The Miller's Tale" who goes apparently unpunished at its conclusion. In her portrait at the beginning of the tale, the narrator is satirizing a medieval literary device called a blazon. This is a section of a romance or short poem in which the poet describes a woman's body by comparing parts of it with other objects. A typical blazon might compare a woman's eyes to the stars, her hair to golden flax. Alisoun's blazon compares the parts of her body to decidedly less glamorous things: her body is like a weasel's, her song like a barn-swallow's, her spirit like young colt's.
What's up with all the animal comparisons? The best clue comes with the last one: she is a "piggesnye [tender chicken]/ for any lord to leggen in his bede" (160-161). This comparison links Alisoun's animal nature to sexuality – animals are unable to control their lust and so, we assume, is Alisoun. Another important aspect of this blazon is its description of Alisoun's "lendes," or loins, or the place where her shoelaces end high on her legs. By drawing the reader's attention to Alisoun's most sexual parts and describing her in animalistic language, the blazon makes Alisoun's sexuality her main character trait.
"And sikerly," we learn, "she had a likerous eye" (136). Alisoun is a lustful young thing, says the narrator, and unlike her husband, whose behavior contradicts the narrator's description of him, Alisoun's only confirms it. She takes up with Nicholas after only the tiniest protest, even going so far as to subject her husband to trickery and humiliation in order to spend the night with Nicholas in their bed.
At the same time, we are discouraged from judging Alisoun too harshly. She is consistently described as an animal about to be ravaged. Just as she's a piggesnye "fit" to be laid in a lord's bed, she's a colt ready to be tamed when Nicholas wants her and a mouse about be snatched by the cat Absolon. These metaphors have the effect of turning Alisoun into an object that's meant to be ravaged by the men around her, rather than a person who makes her own decisions about her sexuality. Alisoun's betrayal of her husband, these descriptions seem to be saying, is beyond her control: it's her nature, her fate.
Alisoun's character borrows a lot from misogynistic stereotypes about women, which portrayed them as dangerously lustful liars and cheats. The interesting thing about her portrait, though, is the way it not only compares her to animals, but also to animals that are attacked by predators. Comparing women to animals was common (animalistic = lustful), but the way it's done here, it also subtly makes us think twice about who's a victim in this story. Do we blame the mouse for being eaten by the cat? We're not saying that Alisoun's character is exactly sympathetic or admirable, just pointing out the way the language used to describe her makes us think twice about the stereotype it relies upon.