WEBINAR: VIX On Five Highly Active Stocks, Weds., October 3 at 6pm ET w/Mark Sebastian and Jill Malandrino. CLICK HERE FOR INVITE AND TO REGISTER.At the Value Investing Congress on Tuesday, fund manager David Einhorn made a short case for shares of Chipotle Mexican Grill (CMG), arguing that Yum! Brands! (YUM) was going to succeed at taking market share from the burrito-maker with its new Cantina Bell line at Taco Bell. Shares fell 6% in the moments after it became clear that CMG was Einhorn's target, as he has developed a reputation for successfully shorting high-priced stocks. The stock closed down 4% on the day, and short option-implied volatility rose 8%. CMG is down nearly 14% over the last twelve trading sessions, and is down more than a third from its high set back in April.