That's what makes them useful. You can fake taking a ninja tool from your pouch where in reality you create this and throw it. They won't pay attention to it if they think it's a regular kunai and you throw it in front of them.
Oh shit.
Ototon/Genjutsu: Doppurā kōka | Sound/Illusionary Arts: Doppler Effect
Type: Supplementary
Rank: B-Rank
Range: Short-Mid
Chakra: 40 Chakra
Damage: N/A
Description: After shooting or throwing a projectile or ninja weapon, the user uses the sound of the moving object as a trigger for a powerful illusion. The sound of the object would not be enough on it's own to trigger the illusion, so the user has to use his chakra in order to amplify the sound. The powerful illusion consists of tricking the opponents hearing, using the basic principle of incoming sound, called Doppler effect. The doppler effect works by making the sound of an incoming object much louder than it is, as it's moving away from the person. This happens because the sound waves of the incoming object get shorter and shorter as it's getting closer to the listener and longer and longer as it's receding. Using his ability to control sound with his chakra, the user would disturb the opponents chakra flow, causing confusion in his hearing and making incoming objects appear much closer. Using the genjutsu he can also make the opponent hear the object coming from behind, or any other side of choice. The purpose of this genjutsu is to effectively confuse the opponent and trick his senses, making him unsure whether to trust his hearing or vision, giving the user a short window to take advantage against the opponent.
Note: Usable only twice per battle
Note: Only McRazor can teach this
And then some water for a boom boom.