Here's why:
* Figurative Language: The phrase is a metaphor. The creature's eyes are being compared to flames, suggesting they are bright, intense, and potentially dangerous.
* Fearsome Appearance: The "Jabberwock" is described as a monstrous creature, and its fiery eyes contribute to this image of fear.
* Threat: The eyes foreshadow the creature's potential for harm. The flames suggest burning or destruction, hinting at the danger the Jabberwock poses.
The phrase "eyes of flame" is a powerful image that captures the reader's attention and emphasizes the Jabberwock's menacing presence. It adds to the poem's whimsical yet eerie tone.