Anyone who spends any time on a mountain bike riding real trails comes to expect encounters with wildlife. I've nearly smashed into countless bobcats and deer. I've run over a rattle snake (on accident), and probably many of his reptilian cousins. I'd never do it on purpose though. But when you're on a road bike, you generally don't think of animals as a concern. In my case I'm much more worried about cars and careless drivers, drunkards and cell phone talkers than anything with four legs. I did get into a bike-totaling crash with a bicycle cop on the Golden Gate bridge, but that's a story for a different post.
When I lived in Boulder, Colorado I was blazing down a hill (on the bike that was later totaled in SF) just after dark at the end of a ride, and an adult male elk walked out into the street. I didn't see him until I was about a foot from him. Luckily I missed him by about six inches, because if we had made contact I have a feeling the photographic evidence would be a lot uglier than this pic from Blue Collar Mountain Biking.
Squirrels are always so indecisive! And I've always had a hunch that bladed spokes are dangerous!