Kiwi forage at night by walking slowly and tapping the ground, then driving the long bill into soil and leaf litter. The nostril openings at the bill tip put the olfactory apparatus directly against the substrate being probed, and the bird frequently snorts to clear them.
The brain matches the behaviour. Kiwi have unusually large olfactory bulbs relative to brain size compared with most birds, and experiments have shown they can locate buried food by scent alone. Sensory pits at the bill tip also carry mechanoreceptors, so probing likely combines smell with detection of prey movement. Their eyes, by contrast, are small and their vision is poor.
A persistent misconception is that kiwi are blind or nearly so. They are not; their eyes function, they are simply small and of limited use to an animal that navigates a dark forest floor largely by smell and touch.