Mark thinks that, after passing the original negative around to show witnesses there was no trickery with a bit of sleight of hand Mumler could have slipped the ghost negative underneath the portrait negative.
Although some of its ministers may stay, its departure increases the chances that Ms Rousseff will be impeached on charges that she used accounting trickery to disguise the size of the budget deficit.
Researchers in Australia have been devising and testing a method of trickery to make lions think they are being watched by the painted eyes on cow butts.
It also involves attacks, trickery and deceiving an opponent and can be imagined as a strategy game that also requires significant technical prowess to pull off the most spectacular moves.