The following passage (paragraphs 21-23) adds to the development of the story mainly by

We are very miserable,” said Darzee. “One of our babies fell out of the nest yesterday and Nag ate him.”

“H'm!” said Rikki-tikki, “that is very sad—but I am a stranger here. Who is Nag?”

Darzee and his wife only cowered down in the nest without answering, for from the thick grass at the foot of the bush there came a low hiss—a horrid cold sound that made Rikki-tikki jump back two clear feet.