https://www.reuters.com/article/us-retail-trade/gamestop-reddit-rally-stocks-slide-more-yellen-vows-scrutiny-idUSKBN2A40Z0 >Shares of GameStop Corp and others favored recently by retail investors fell further on Thursday, while U.S. Treasury Secretary Janet Yellen said she needed to "understand deeply" the trading frenzy that has gripped Wall Street.