As I was spinning, I saw a nice bright flash from my camera. Even though I couldn't be sure where it hit exactly, I was pretty sure it hit the lens. When I took a look, sure enough, there was a chip in it (well, what I thought was a chip at the time anyway.) When I was able to pull this shot up on a large screen it was pretty obvious where it was hit (check out the faint blurry, angled streak near the top right.)
I cleaned the lens and could feel texture from the spot so I was pretty sure it had gotten pockmarked, but when I took a macro shot I could see the texture was outward instead of inward. It wasn't a chip. It was molten steel that hardened and stuck when it hit the glass. So now I'm working on finding out how to best remove it with minimal damage to the glass... Suggestions?