Art Cashin said a "danger" in China that could flare up if copper prices continue to tumble may contribute to a "bumpy couple of days" on Wall Street.
Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday that in China, "Copper isn't just a metal used in making products. It is collateral in a lot of the 'shadow' banking loans. If the value of your collateral goes down the banks either ask for more collateral or can call your loan."
Those fears, Cashin said, are bringing back memories of the negative "spillover effect" in 2008 as housing loans went bad, "so they're trading very nervously."
—By CNBC's Alex Crippen. Follow him on Twitter