When you use 'yahoo answers'(no single quotation marks) as a search term to run a Google search, the 6th result is Yahoo! answers-wikipedia,the free encyclopedia, whose URL is en.wikipedia.org/wiki/Yahoo!_Answers. The snippet is
Yahoo! Answers is a community-driven knowledge market website launched by Yahoo! on December 13, 2005 that allows users to ask and answer questions posed by ...
But if you use "yahoo answers is" or "yahoo! answers is" and site:wikipedia.org to run another Google search, this result will be missing from the search result set.
http://www.google.com/search?hl=en&newwindow=1&safe=off&q=yahoo+answers+ &btnG=Search
http://www.google.com/search?hl=en&newwindow=1&safe=off&q=%22yahoo+answe rs+is%22+site%3Awikipedia.org&btnG=Search
http://www.google.com/search?hl=en&newwindow=1&safe=off&q=%22yahoo%21+an swers+is%22+site%3Awikipedia.org&btnG=Search
Why does this happen?