grinding sounds while you're not shifting are generally a bad sign

So, a few weeks ago, I gave Gertie a bath. Basically, I took her rear wheel off, took the rear dérailleur off, degreased everything, put it all back together, and lubed her back up. She seemed to respond well to the attention, and she was shifting a lot more smoothly.

Last night as I was coming home, I noticed that her chain was grinding, as if the shifter was mis-aligned. It was late, so when I got home, I grumbled at her, and put her in the garage and went to sleep. Today, she was still growling at me while I was riding into work. When I got to work, I took her upstairs and parked her in the computer room. As I was gathering my things to go into my office, I noticed that her rear dérailleur was missing a cogwheel. Yes, folks, that's right. She hobbled back and forth to campus on one cogwheel. Apparently, I didn't tighten down the bolt which holds this particular cogwheel in, so after riding for a few miles, it decided to pop out.

Needless to say, Vince gave me a ride home. We stopped at a bike store and I bought a new dérailleur set for $30. It sucks that I'm going to have to junk the one that's already on there. On second thought, I could just grab the missing cogwheel from the new one and replace it. That way, in the not-too-likely-but-still-possible event that I find the cogwheel (I think I've got a pretty good idea where it popped out) I can use the new dérailleur for Bucephalus.

Speaking of Bucephalus, I bought a rear tire for his rear wheel. Now all I need is a chain, an inner tube, a seat, and some new cabling, and he'll be ready to go.