But, I wonder what he saw/heard. Like when the dog barks at something that I can't see or hear, I am sure that it's something, but what? The squirrel thought that there was danger. Something made him feel that way.
Perhaps he saw something...bird or plane...overhead, but it kept going, so you didn't see it, and it made him so nervous that he didn't stop worrying until you assured him that all was well.
Was this a young squirrel, as in from this year, or an older squirrel, do you think?
Hopefully, a molt...
Love All Life; Thank You For Posting! :)