A formidable force is encroaching on the home listing leader's turf.Shares of Zillow Group (ZG 7.90%) (Z 8.47%) fell on Monday following reports that Alphabet was entering the online real estate arena. By the close of trading, Zillow's stock price was down roughly 8% after falling nearly 13% earlier in the day. A new competitive threat Google is reportedly adding home sale listings directly to its search results in select markets.The tech titan appears to be testing demand for the new features, which inclu ...