
I can hear them!
I also know people who blow them, get no reaction so blow again harder, and harder and harder.............Dog eventually comes back but it has feck all to do with the whistle blowing as the dog has no idea what it means!
Now I find the noise irritating and I ONLY hear it as a very faint high pitch whistle, but it clearly is upsetting to horses (have witnessed a brat with one in a barn full of stables, they were all getting increasingly upset, till I requested said brat stopped blowing it before I inserted it somewhere.......

).
So I guess what the OP is getting at is why keep blowing a dog whistle if the dog is not responding to it! Bit like the owners that scream fido's name louder and louder as it fecks off it the opposite direction.....POINTLESS!