As an oldman told,
who hit his enemy in fighting, it's like a eagle that fly on a bird
As said by one of the elders, the one who strikes the enemy on the
battlefield can be compared to an hawk which strikes a bird.
Besides a swarm is made of thousand birds, the hawk focuses only on its prey.
The sentence 'Kezue no kubi' indicates the hit on the head after having
declared 'I'll hit that very warrior who's wearing that armor'.