Nag and Nagaina are two cobras featured in Rudyard Kipling's short story "Rikki-Tikki-Tavi," which was part of the author's work called The Jungle Book.

In this story, the title character is a mongoose who saves the family from the cobras. Nag is the male cobra, and Rikki-Tikki-Tavi attacks him when in the bathroom after Nag and Nagaina have plotted a sneak attack against the family. Rikki-Tikki-Tavi finds Nag in the bathroom sluice. A sluice is an open channel for water to go through. Rikki-Tikki-Tavi bites Nag on the head and is thrashed about by the snake until the "Big Man" in the house shoots the snake. Below is the description of where Nag was before Rikki-Tikki-Tavi attacked him:

He stole off to Teddy's bath-room, but there was nothing there, and then to Teddy's mother's bath-room. At the bottom of the smooth plaster wall there was a brick pulled out to make a sluice for the bath water, and as Rikki-tikki stole in by the masonry curb where the bath is put, he heard Nag and Nagaina whispering together outside in the moonlight.

Nagaina engages in a fight with Rikki-Tikki-Tavi on the veranda of the bungalow where the family lives. She is seeking revenge for Nag's death and targeting Teddy, the child in the family.

Teddy and his mother and father were there at early breakfast, but Rikki-tikki saw that they were not eating anything. They sat stone-still, and their faces were white. Nagaina was coiled up on the matting by Teddy's chair, within easy striking distance of Teddy's bare leg, and she was swaying to and fro, singing a song of triumph.

She takes the fight to a hole underground in the garden, and it is there that she dies.