General Motors (GM, news, chart, volatility) is helping pull the Dow Jones Industrial Average under water Monday afternoon. GM is down 19 cents to $5.60 and falling to session lows after reporting a 45 percent drop in October North American auto sales. Analysts were looking for a 43.3 percent decline. Rival Ford Motor (F) reported a 30.2 percent drop, which was less than the 36 percent drop the Street was expecting. Trading in the options market seems to reflect a sense of disinterest, with 28,000 puts and 23,000 calls traded across the entire automobile and auto parts sector by 2:00 ET Monday.