The kiwi's beak is the perfect piece of hunting apparatus to sniff out and probe for its prey.

Its ability is nothing to sniff at.  The kiwi has the second largest olfactory bulb among all birds, relative to the size of its forebrain.  It is beaten by a smidgeon by the condor.

Because much of the kiwi's food lives below the surface of the soil or in the leaf litter, its highly developed sense of smell is vital.  As it walks it taps the ground with its beak, probing the soil and sniffing loudly. 

Its sensitive nostrils can locate an earthworm up to three centimetres underground.

A Probe and a Lever
Once a tasty snack has been located, the kiwi pushes its beak deep into the earth, sometimes right up to the hilt. To protect the opening, the tip of the upper mandible overlaps the lower one.

The kiwi may use its bill as a lever, moving it back and forth to widen the hole.  Kiwi may even use their entire weight to drive the bill deeper, kicking up their legs in a kind of head-stand.

But once it has hold of the worm, the kiwi moves very delicately – worms break easily.  Sometimes a steady pull will do the job.  Sometimes the kiwi remains motionless until the worm relaxes its grip on its burrow.  At this moment the kiwi gives another pull and usually succeeds in catching its prey.

Sniffs and Snorts
Having nostrils at the end of its beak help kiwi make the best use of its ground-based habitat.  Evolving the ability to sniff out prey and extract it from the ground easily, gives kiwi an advantage over other birds.  But this hunting strategy has its drawbacks. Kiwi can often be heard snuffling and snorting loudly to clear dirt from its nostrils.