From Creatures Wikia
Indio Norns are less prone to infections than most norns - they can eat garbage and detritus, and breathe under water. Poisons and infections aren't such a problem as for "normal" norns. In short: Indio Norns don't feel much pain. They don't have a favorite place to stay so you can meet them at almost any place and they feel comfortable almost anywhere. Most of the time they remain content and happy, but of course they need a good food source and some toys to play with!
- Detailed description of how Indio Norns fight off poisons (translated by Babelfish)