I have a Great Pyrenees. They have been bred to protect livestock, but they will protect ANYTHING. When you live with one awhile, you realize that they are like Homeland Security, they have threat level warnings.
Last Monday evening, my MIL and I were alone in the house. Her suite of rooms is at the opposite end of the house from our bedroom and office. Atticus started sounding off like all the Devils in hell were coming. When I checked on him he was standing by MIL's door.
When I opened her door she was grey and gasping for breath. While I called 911, tried to find my husband, etc , Atticus stood in the middle of the great room and barked at the ceiling.
I have to believe that he understood our fear during those moments.