Visticia, an automated dow sell off happened in 1988. At a certain point on a certain day, a Tuesday I believe, a computer miss read a market indicator eg. that option day of the month and sold a lot of stock. Other computers miss read read this and sold heavily.
Billions of $$stock were sold as stops were reached. Just like the ping pong ball and the mouse traps.
For other explanations see my post above.
