Nag and Nagaina are two cobras that live in the garden outside the bungalow where Rikki has come to live. Nagaina is "Nag's wicked wife." Nag and Nagaina are also father and mother to 25 eggs that are almost ready to hatch into their "children." At the beginning of the story, they act together as a team to try to kill Rikki. While Nag speaks to him, Nagaina sneaks up behind him and strikes. Darzee has warned Rikki in the nick of time.
Nag appears to be the more formidable adversary physically, but Nagaina is more sly. One might say Nagaina is the brains and Nag is the brawn, or Nagaina is the villain and Nag is the less intelligent sidekick to the villain. This relationship is apparent when Nagaina is explaining to Nag that he should bite the man first, then come outside so the two of them can fight Rikki together. Nag questions whether it is necessary to kill the people, and Nagaina explains that only when the bungalow is empty will they be "king and queen of the garden." This shows she is the one who creates the strategy. When Nag is killed, Nagaina mourns for him at the rubbish heap, and she seeks revenge on the people for killing Nag and making her "a widow."