Three images of a Cooper's Hawk and a Gray (black) Squirrel having a stare-down on top of our fence. The top of the fence usually belongs to the Squirrels, but this time there is a slight obstacle in the way; namely, an adult Cooper's Hawk.
Best viewed in original size. (Top two images are a pano of two images. All images taken through double glass sliding doors.)
Top Image: The Squirrel holds back as it natters at the Hawk.

The Squirrel continues its nattering as it slowly advances towards the hawk. The Hawk seems surprised and unsure of what to do.

Suddenly, the Squirrel jumps forward towards the Hawk, but into the bush, apparently trying to get around the Hawk. The surprised hawk takes off to perch in an other tree.
I saw a similar encounter between a Squirrel and a young hawk about a year ago - with the same result; namely, the Squirrel charging and flushing the young Hawk.
Note: I first thought that this was a juvenile Hawk, however, as Tom Munson pointed out in my next posting, it is actually an adult. So, why was it afraid of the squirrel? I'm wondering if it might have an injured foot as not once in the 10 minutes or so I watched the action, did I see it's other foot. i was always standing on one.