Yesterday's trading session saw bonds improve in the afternoon despite a complete absence of overt justifications.  That's not to say they don't exist--simply that they're not the sort of cut and dried factors like scheduled economic releases, Fed comments, or viral newswires.  Today's session is seeing the opposite move for reasons that are just as mysterious.  Neither example has been very big, so they're not worth losing sleep over.  More importantly, this is exactly the sort of random volatility we expect to see in the 2nd half of December.  For many traders, these two days have been the last two days of the year.  The net effect of the past two days is that rates have been coasting along a floor of 3.89% in terms of 10s and haven't moved more than a few bps in either direction.