In book I, canto I, stanza XVII of The Faerie Queene, the knight Redcrosse has just entered the den of the monster, Error. Although this is not his quest, and he has stumbled upon the monster by accident, he determines to attack her anyway. The stanza begins with him doing so. Rather confusingly, Redcrosse is described in the first line of the stanza as "the valiant elfe," referring to his elfin or "faerie" ancestry.

The monster has the upper half of a woman and the lower half of a serpent, and is called "she" by the poet. Redcrosse uses "his trenchard blade" to bar her path out of the den. She threatens to sting him with her tail, and he makes a thrust at her with his sword. The blow glances off her head but hits her shoulder.

In stanza XVIII, Error counter-attacks, lifting her serpent's body off the ground and winding it around Redcrosse's body. Redcrosse is trapped, unable to move hand or foot. The last line, "God helpe the man so wrapt in Errours endlesse traine," makes clear the allegorical meaning of the passage (as though a battle with a monster called "Error" really needed this explanation).

In stanza XIX, Princess Una, who has been traveling with Redcrosse and witnessing the fight (which she tried to dissuade him from seeking), now calls out to him with advice:

Add faith unto your force, and be not faint:
Strangle her, else she sure will strangle thee.

Redcrosse hears this and is suddenly angered. With all the force at his disposal, he frees one of his hands, grabs the monster's neck and begins to strangle her, so that she is forced to loosen her grip on him. This is the beginning of the monster's defeat, graphically described in the ensuing stanzas.