Courtesy of Sully:
This is a picture of the ratio of Mousavi vs. Ahmedinejad votes throughout the counting process. The smooth, uncurving slope means that as votes for one were added, votes for the other were added in proportion; and THAT means that throughout the counting process the percentage by which Ahmedinejad was winning didn't change at all. Ever.
This isn't even unlikely. It's impossible.
And here's what the people think of it: