Calling any story a fable puts it in a specific category of literature. Fables are allegories, stories that use animals as characters with the plot written "so as to reveal some truth; ordinarily that truth concerns a particular aspect of human behavior."
"Rikki-Tikki-Tavi" certainly qualifies as a fable. The story presents the value of being brave, loyal, and determined, as demonstrated by the battle between Rikki and the cobras, Nag and Nagaina.
Rikki-tikki looked at his big back, wondering which would be the best place for a good hold. "If I don't break his back at the first jump,'' said Rikki, "he can still fight; and if he fights -- O Rikki!...It must be the head,'' he said at last; "the head above the hood; and when I am once there, I must not let go.
Rikki intuitively understands the threat posed by the cobras and recognizes the response he must make. He develops his plan of attack carefully, selects the best moment to execute it, and fights with great valor. Rikki establishes his area of responsibility, frees his people of danger, and insures that they remain safe after the end of the story. "he kept that garden as a mongoose should keep it, with tooth and jump and spring and bit, till never a cobra dared show its head inside the walls."
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