No experience with squirrels, but lots with groundhogs. The worst was as a kid on BMX bikes. My buddy was up ahead and decided to use a dead bloated G-hog as a jumping ramp. Yes, you can "get guts on your face". He starts puking cause of the messy stuff covering him and the bike. I puke due to the pure stench.

I had a hog jump in front of my car while going down the highway @ 60mph. He dodged back and forth and my last ditch effort was to straddle the poor guy and hope he ducked. Well, he didn't. A quick look in the rearview showed a hog standing on his head spinning like a top. I didn't know hogs could breakdance!!

Aside from that, its just been a couple of snakes out here in the phoenix dessert. That scares the heck out of me as they usually strike at the bike with their dying effort.