On the surface, this may LOOK like a regular whistle... It is, however, the 'only' operational Ninja Whistle in the entire universe.
When blown, the whistle emits a powerful sonic boom at a frequency only the mystical ninjas (with their highly advanced hearing abilities) are able to detect.
Once summoned, you, with your imperfect non-ninja eyesight, will not be able to SEE the stealthy ninjas... but they'll be there.
Oh yes... they'll be there.
1 -This whistle summons Ninjas.
2 - Can YOU summon ninjas?
3 - You cannot.
...UNLESS YOU BUY THIS WHISTLE.