A claw-hammer.
Didn't see it till the last second and was too late to swerve. When I hit it I heard this clack-clack-clack sound. I thought, Oh crap, the hammer is wedged between the tire and front fender and tearing the heck out of my bike. I stopped as fast as I could. Looked down, and what had happened was the hammer had ripped the spring off my jiffy stand and the stand was flapping up and down. I was afraid to ride it like that for fear the flopping jiffy stand would wreck me. I was afraid to set the bike on the jiffy stand because I wasnt sure if it would hold the bike up without the spring ( later found out that it would stay up without the spring). I was by my self, so I called my son on my cell and waited on the side of the road sitting atop the bike holding it up for 30 minutes until he came and taped the jiffy stand up with electrical tape so I could ride the bike home. We found the spring on the side of the road, as well as a perfectly good claw hammer. The spring was heck putting back on. I now carry electrical tape and a few zip ties in my windshield bag in case it ever happens again.