User blog comment:Lifebleedin/how does killua know zenos ability/@comment-24461729-20140124141336

zeno is a transmutator, and while dragon dive may look like a conjurer ability, it is a transmutator one.....the only way to hide nen to the point where gyo has to be used is the use of the technique "In".....

zeno probably cannot use "in" because of the large scale of this attack.....in other words if hisoka used his bungee gum without "in" other people would be able to see it.

Now can normal people sense "aura"? if u remember in tht filler episode where gon or someone mentioned tht people unknowingly leak out nen even if they have not awakened it....(The episode where zepile makes something while not knowing anything about nen)

Considering killua's training i won't be surprised if he could sense or see nen at a young age....