It is funny what sets them off. Simba is pretty chill about most things, although he was definitely not happy with hay bales out in the field the first time he saw them. And the first time he saw a friend of mine he was uncharacteristically barky, of course this is the friend of mine most scared of dogs. Later on I realized it was probably because she was wearing a fake fur coat, and it was likely the first time he had seen a strange furry human...couldn't blame him, really. I'd bark at a Sasquatch too....
When my niece was little and her Uncle wore a dark fur hat she cried, she thought he had the cat on his head