Markets | Wed Oct 21, 2015 3:40pm EDT The S&P 500 and Nasdaq slipped in choppy trading late Wednesday afternoon as insurers and other big healthcare names dropped and Yahoo (YHOO.O) shares fell following disappointing results. Valeant Pharmaceutical’s (VRX.N) U.S.-listed shares dropped sharply, hitting a low of $88.50, after short-seller Citron Research released a report…