The US Chamber of Commerce, normally not known for spreading global warming awareness, shows the predicted water level in Chicago by the year 2050 in the twitter post below. "Mark Twain," according to Wikipedia, refers to "the cry for a measured river depth of two fathoms."
But seriously, Twitter doesn't quite have this "inline image" thing down yet. It auto-crops images appended to tweets rather than shrinking them, resulting in unintentional droll humor such as the removal of the Mark Twain quote in the above example.