Investors tend to be jittery in October, a little more on a hair-trigger than usual. They just need something to set them off. Two possibilities: 1) China starts shooting or "disappearing" protestors in HK, possibly justified by a false flag incident or violence instigated by secret police embedded within the student groups. 2) Ebola in the U.S. causes public panic, people stop flying and fearful employees stay at home. Businesses go under.