There are two passages early in the story that establish that mongooses in general are natural enemies of snakes. The first is by Teddy's father (speaking of Rikki-Tikki) "Teddy's safer with that little beast than if he had a bloodhound to watch him. If a snake came into the nursery now --- '' and the second is from Rikki-Tikki's initial meeting with Nag "and he knew that all a grown mongoose's business in life was to fight and eat snakes"
Darzee, Darzee's wife, Chuchundra, And Teddy's father
First, because Rikki is a mongoose. And mongooses fight snakes. Second, Rikki knows the snakes plan to kill the people, and Rikki likes the people.
Nag and Nagaina two King Cobras.
Rikki-tikki fights 3 snakes, a Karait and two cobras Nag & Nagaina
The Heat is on from season 2 ;)
the big man shoots nag while rikki was fighting with him as for nagina they fight after the fight she takes the last remaining egg of already destroyed eggs and reatreats to her den with rikki following they fight underneath the ground unseen the next day rikki climbs out of the hole claiming the cobra will never come out again giving us a hint that rikki bit killed her along with the last egg
Rikki-tikki was fighting because he didnt want anything to happen to his newly found family
Because Nagaina was going to bite the little boy that found Rikki and then they were gonna fight but Rikki got one of Nagaina eggs and was gonna smash it but Nagaina didn't want him to so she give up and ran away into a house and Rikki ran after.After night Rikki never came out and every animal thought he died but when they were about to leave Rikki came out and killed Nagaina. Then the garden became safe and there was no more killing again.
In the great war, Rikki-tikki fought Nag and Nagaina. Rikki-tikki fought the great war against the cobras who planned to kill the family in the big bungalow.
to live the mongoses alone and to save the garden
Nag and Nagaina were King Cobras.
They begin a fight