I actually ran over and killed a squirrel on my bike a few years ago. I was riding down a steep hill pretty fast, a squirrel chased another one onto the street in front of me, and I caught the chaser on the neck before I could slow down. I heard a little popping sound, and I'm pretty sure I broke its neck. I kept going and didn't dare look back. It was pretty disturbing, but I got over it pretty quickly, because, honestly, I don't much like squirrels anyway. If they didn't have furry tails, we'd recognize them as the tree rats they really are.