Question

Why do dog owners use a whistle that they can't hear?

Answer 1

dog owners use the whistle to call them because dog,s can hear more than an human that's you know they say that when any type incident like tusnami Earthquick is goning to happen dogs run before

Answer 2

dogs owners use a whistle because the dogs have a great capacity of hearing the sounds, when we use the whistle then the dog can understand that we are calling it so it comes running. the reason behind the usage of the whistle is the that the whistle works like a  code language. I do have a pet dog to communicate with it in the code language is used often. to do tricks or even to ask him to do something the whistle is used by me.
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hope so my answer is useful and mark as best if possible ...^_^