Science and Pets - How Do Do Whistles Works?

Science and Pets - How Do Do Whistles Works?
1.  You blow as hard as you can on your shiny new dog whistle.  You can't hear a thing.
2.  Fido see you blowing on a whistle that doesn't make any noise.
3.  He runs to you and barks until you stop, because he thinks you've gone insane.