From Creatures Wiki
Hunger is the biological drive to eat food. Creatures instinctively seek out food to sate their hunger - in the later games, they can use their sense of smell to aid them in their search. Some foods, like honey, provide a false sense of satiety, having a disproportionately large amount of Hunger-- in contrast to the amount of nutrition they provide.
In C3/DS, the digestive system became more complex, and three distinct kinds of hunger were recognised by creatures:
- Hunger for Protein - most norns will instinctively seek out fruit or food-category items to satisfy this drive.
- Hunger for Carbohydrates/Starch - most norns will instinctively seek out seed or fruit-category items to satisfy this drive.