I do a spitting hiss at squirrels and cats by the side of the road. It usually scares them back into the bushes.

And, similar to a velocity's post, I was riding on the Little Miami Trail a few years ago, heard a crack of a branch breaking, and had the branch end with a squirrel hanging on land a few feet to the side of me.

I've seen other photos of squirrels caught in spokes. They can be dangerous.

This made me laugh: