By Chris Lau for Kapitall. Whenever a stock’s price falls a lot over a short period of time, it may represent a buying opportunity, but it may be a sign that the company’s fundamental health is in question. A stock is a possible buy if the selloff was irrational, but if investors discovered something untoward in the company’s numbers, they should stay away from the stock until its irregularities are smoothed out. Two stocks giving investors pause are NQ Mobile ( NQ ) and Vringo, Inc. (VRNG). Bears have latched onto bad news that things are not right at NQ Mobile. Its CFO resigned, apparently for family reasons. Last month, NQ Mobile dismissed its auditor, PwC, though NQ claims there was no dissention in PwC’s work. Investors had high hopes for NQ twice in the past two years. The stock peaked on October 14, 2013, closing at $24.92, and again at $18.28 on March 10, 2014. Since then, the stock has been in free fall NQ rose nearly a quarter at the end of July, when NQ said it received a non-binding proposal from Bison Capital. The offer was $9.80 per share. NQ Mobile’s short float stood at 52.13 percent. Vringo plunges 72 percent In the intellectual property monetization space, Vringo plunged after the federal appeals court ruled against it in its patent dispute with Google ( GOOGL). The full ruling is available here. Earlier last month, Vringo had said it expected confirmation from the USPTO for its patent validity. If the ruling was in Vringo’s favor, the firm would have earned a running royalty for Adwords, amounting to of 1.36 percent of sales. Caution Warranted The warning comes too late for current shareholders in the two companies. Still, investors thinking they see a deal should think twice before starting a position Vringo or NQ Mobile.