Take a look at the sentence again:
Josie, Don's Cairn terrier, will bark at anything that
moves, squirrels, wind blown leaves, passing
cars, and her own shadow will start her yapping.
For a sentence to be fused, you must have two complete sentences run together with no punctuation. In the example above, a comma joins the two sentences. Josie, Don's Cairn terrier, will bark at anything is one sentence. Squirrels, wind blown leaves, passing cars, and her own shadow will start her yapping is the second sentence. Thus, this error is a comma splice.
Remember that both comma splices and fused sentences are major errors. They make your reader think that you cannot write a correct sentence. Because the sentence is the most basic building block of a piece of writing, comma splices and fused sentences make you look like an amateur!
To fix the problem above, you could put a semicolon between moves and squirrels.