Take a look at the sentence again:
The problem occurs between moves and squirrels. Josie, Don's Cairn terrier, will bark at anything is a complete sentence. Wind blown leaves, passing cars, and her own shadow will start her yapping is another complete sentence. Because these two parts have just a comma between them, they create a comma splice, a major sentence error.
To fix the problem, you could put a semicolon between moves and squirrels.