My Otis...

Despite the fact that he weighs in at a whopping 16lbs, he has the ferocity of a bear... Unfortunately, it also comes with the intelligence of a squashed grape.
He doesn't hear too much of anything any more and he usually barks randomly at the noises in his head, but when he SEES something with his failing vision, he'll let it know he saw it by barking at it. It could be a person, another dog, a bush, a squirrel, a rock, a car, a house, me... It doesn't matter. Hackles raised, barkity bark bark bark...
These days, because of his advanced age, he'll bark at it, and then forget what he was doing within a few seconds. It works out well. He'll be barking away, stop to sniff the ground and forget what he was doing.  <Sigh>  But whatever it was that Otis was barking at KNOWS that he thinks he's a vicious, scary animal.