I was out geocaching on a trail one time in the early fall and a squirrel was digging in the leaves, making a lot of noise. I worked up really close to it and was not noticed until I was about 5 feet away. It looked up and bolted, jumped for the little tree....and missed. Landed with a thud, rolled, got up, looked around like "What the hell??" and scrambled off to another tree.
Another time, I was sitting in a tree stand, and a couple of squirrels were chasing around in the trees next too me. All was going well, until I heard a thump and something hit the leaves below. Looked down, one of the squirrels had fallen out of the tree and was laying on the ground dazed. It got up, looked around confused and then scurried back up the a tree.