"Good gracious," said Teddy's mother, "and that's a wild creature! I suppose he's so tame because we've been kind to him." (11)
The story sets up the British family as kind and generous people. But if we read the family as representing Britain's colonizing power in India, this view is, shall we say, a tad rose-tinted. (See the Sepoy War of 1857 for more.)
"There are more things to find out about in this house," [Rikki-tikki] said to himself, "than all my family could find out in all their lives. I shall certainly stay and find out." (14)
British civilization lures Rikki-tikki in. Hey, we like cool new gadgets too, but Rikki-tikki does act a bit like a cultural sell-out.
Then Rikki-tikki went out into the garden to see what was to be seen. It was a large garden, only half cultivated, with bushes as big as summer-houses […]. (18)
As we mention in our "Setting" section, the uncultivated aspect of the garden signifies the wilder nature of the Indian wilderness. Rikki-tikki's taming of it—of India —consists of the bulk of the conflict.
"We are very miserable," said Darzee. "One of our babies fell out of the nest yesterday and Nag ate him." (21)
As we mention in our "Characters" section, the cobra and Indian culture are inseparably linked together. The story sets up Nag as a baby killer very early, and the postcolonialist might read this as the story suggesting that Indian culture has a similar primitiveness and barbarity.
[…], and he looked at Rikki-tikki with the wicked snake's eyes that never change their expression, whatever the snake may be thinking of. (23)
Here's another example of the story making Nag out to be the bad guy. These snakes just can't catch a break with Rikki-tikki or the narrator.
Teddy carried him off to bed, and insisted on Rikki-tikki sleeping under his chin. Rikki-tikki was too well bred to bite or scratch […]. (39)
The narrator claims Rikki-tikki is too well-bred to bite or scratch but try telling that to the snake he just killed. No, Rikki-tikki only refrains from scratching the British family. He threatens all other matter of animal with violence, including Darzee and Chuchundra.
The big man had been wakened by the noise, and had fired both barrels of a shot-gun into Nag just behind the hood. (61)
The power of the British colonizer is represented in the barrel of a gun. Notice how the father keeps control in his garden only through violent methods?
[…] "and Nag came out on the end of a stick—the sweeper picked him up on the end of a stick and threw him upon the rubbish-heap." (68)
If we read the cobras as a symbol of Indian culture, this quote should come across as historically telling.
[Rikki-tikki] bit off the tops of the eggs as fast as he could, taking care to crush the young cobras, and turned over the litter from time to time to see whether he had missed any. (85)
Of course, the killing of babies is only seen as a bad thing when Nag does it. Somehow, Rikki-tikki's murder of way more (potential) babies becomes a heroic act.
Rikki-tikki had a right to be proud of himself; but he did not grow too proud, and 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 (111)
Rikki-tikki for the win. He successfully beats back the advance of India's nature and guards those the walls set up by the British family help keep it out.