Just a little lesson learned. Dropped the drive chain today. In putting it back on I reached through from the left side of the bike without even thinking about it. As the chain went on, and I pulled my hand back, my index finger got caught between the timing chain, and the spinnning chain ring, creating a nice little puncture wound where the tooth went into my finger.
In hindsight, it was obviously stupid to reach through from the left (or at least, not through the timing chain.)