Chuchundra, the sniveling, fearful muskrat who creeps around walls because he is too terrified to go into the center of a room, meets Rikki in the middle of the night. He insults Rikki by begging him not to kill him. He then insults him by suggesting that Nag might mistake Chuchundra for Rikki. He says, "Those who kill snakes get killed by snakes." He issues this warning to Rikki not to help keep Rikki safe but as a way of explaining why Rikki's presence gives him, Chuchundra, more reason to fear.
Chuchundra starts to tell Rikki what Chua the rat told him--but breaks it off when he realizes he might be overheard by Nag. He says, "Nag is everywhere, Rikki-Tikki." Rikki threatens to bite Chuchundra to get him to talk. Even then, Chuchundra won't overtly reveal any information. But he does say, "Can't you hear, Rikki-Tikki?" This is enough of a clue for the clever mongoose. He listens carefully and can just make out the "faintest scratch-scratch" that lets him know that Nag is creeping into the bathroom of the bungalow.
Although Chuchundra says what he says more in justification of his own fears than to help Rikki, his comments do serve as a warning to Rikki, and the muskrat does help Rikki locate the snake in the bungalow.