Preferred stock indexes just don't move this much, but the last few sessions' quick decline in the Preferred Stock Index Fund (PFF -1.3%) has left it trading at a slight discount to NAV. Peter Tchir calls it "spiral risk," and it's there when illiquid underlying assets meet a "beta" vehicle meet a crowded trade (and a few more conditions). When does it end? Often after a capitulation day. The Financial Preferred ETF (PGF -1.2%) also takes a hit.