Google knows instantly how much time you spend on a page and how quickly you return to the search results because it is a useless copy/paste page from SO.
And probably they track content age too? Since they somehow can lookup by content (they can detect duplicated content), there's probably a date remembered too
So they could know if a code snippet was already X years old? And from where, originally. (Unless it got edited a lot but that's not the case here?)
