"I will go, But there is no need we should hunt for Rikki-Tikki afterward. I will kill the big man and his wife, and the child if I can, and come away quickly. Then the bungalow will be empty, and Rikki-Tikki will go."
Nag is talking to Nagiana from inside the house, he got in through the bathroom sluice. While Rikki-Tikki is watching him.
"If I don't break his back on the first jump...He can still fight; O-Rikki!" Rikki-Tikki said, "It must be the head."
This is when Rikki-Tikki is preparing his attack plan! He was debating on weather to break Nag's back or if he should bite him.
This is the scene where Rikki-TIkki is attacking Nag!