Was almost home (maybe 100 yards from the front door), riding through a sort of park area, and it was pitch black out. I downshifted in front to get up a bit of an incline, and instead of downshifting, the chain came completely off. Great. So I get off, and have to stick my fingers in there to get the chain back on the chainring. But while I am doing this, I notice a really awful odor coming from somewhere. Didn't think that much of it at the time, so I got back on and finished the ride. But that awful odor kept following me.

Turns out I had stepped in some dog doo while I was fixing my chain .

I still need to adjust the front derailer - it has been acting up a little lately, but I haven't gotten around to going in and fixing it.