That's a very good question. Some would argue that it makes perfect sense. Here we have a mongoose, Rikki-tikki-tavi, who's as fierce as they come, just the kind of creature to defend this human family from the dangers of Nag and Nagaina, the two venomous cobras.

Without Rikki-tikki's assistance, it's likely that at least one member of the family would have been killed by the snakes. That being the case, it seems somewhat strange not to take advantage of having a friendly neighborhood mongoose around and use him to protect yourself from these poisonous creatures. Besides, Rikki-tikki's in his element battling Nag and Nagaina; fighting snakes is what he's best at.

On the other side of the debate, one could argue that using Rikki-tikki's instincts in this way is a clear case of animal exploitation. The tough little mongoose may have no problem fighting against deadly cobras, but that doesn't mean he's immune to their venomous fangs. Rikki-tikki could so easily have been killed in his epic showdown with Nag and Nagaina, and one could argue that it's unethical to put an animal in harm's way like this. Even if the animal in question has a basic instinct to attack cobras, that instinct is there for the benefit of the animal, not for humans.