Our dog's strongest sense is their sense of smell (far greater than ours), and I know for a fact that they can hear things that I can't hear.
But - dog's eyesight really isn't their strongest sense. They don't really see as well as we do.
***** Sounds like one of your dogs is barking at something he senses - and the other is a copycat. I have one of those little "copy cats" at my house.
Carol Jean |