Today's selloff comes as no surprise to Forbes contributor Panos Mourdoukoutas. He's noticed a number of warning signs: A slowing global economy and investor complacency over political gridlock for starters. More interestingly, he points out that companies such as Proctor & Gamble (PG -0.1%) and Kellogg (K -0.7%) are unable to pass on material costs for essential items. As production costs continue to rise, they should be able to offset the increase by raising prices, but can't. As we all know, in a consumption-driven economy like ours, a weak consumer spells disaster.