optical illusion

years ago, when I was driving somewhere, I had ella with me by herself.  louie might have been at the vet office for one of his knee surgeries.  she had her head out one window in the backseat and her tail wagging out of the other window.  I didn't even notice it until I saw drivers craning their necks to look at her.  I finally realized what they were looking at and two different guys drove by slowly to make sure it was only one dog!