10yr yields are down more than 5bps now, with the most recent push seen immediately after the 9:30am NYSE Open.  The S&P lost 10 points in fairly short order and 10's rallied from 2.87% to 2.84% at the same time.

There's no singular, obvious market mover in play--especially for bonds.  We've seen a series of big trades in bonds that don't coincide with big moves elsewhere.  That said, the general trajectory of stocks, oil prices, and emerging markets all complement the move.

As per usual, MBS are very much lagging the "risk-off" move in bonds.  Fannie 4.0 coupons are up only 6/32nds.  Unfortunately, that's the way things tend to happen in these situations (i.e. panic selling in stocks, safe-haven buying in bonds, as well short-squeeze, position-driven snowball buying.

For what it's worth, no sooner have I typed all this than bonds and stocks are seeing their biggest bounce since 9:30am (higher yields and stocks).  Put another way, there's an increased risk that the rally has run its course.  We'd need to break back below 2.837% to reignite it.  Breaking much above 2.86% would confirm it's over.