Dogs react primarily to sounds and coustic signals, and not to language.
Therefore the whistle is optimal for training and hunting as the sound can hardly be heard. Its sound is clearly different from the ususal sounds that surround your dog every day.
Please note that a light whistle is completely sufficient, as sounds that are too loud rather frighten your dog.
Dogs have a significantly wider range of sounds and perceive the sounds of a high-frequncy whistle with the same volume as the sounds from a normal dog whistle.
Tip: if the cap cannot be removed, please hold the whistle under warm water.