From Grand Illusions.
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Famous Trick Donkeys is a puzzle that was invented by a man called Sam Loyd back in 1858. Normally supplied as a card which you have to cut into three pieces. Two pieces each show a donkey, the third piece has two riders on it. You have to arrange the three pieces so that the riders are seated on the donkeys.
Sam Loyd sold millions of these cards, and at one point they were used as advertising for the P T Barnum circus.
Two of the cards show a donkey standing upright. However hard you try, you cannot get a rider to sit on that donkey! You need to place the riders in such a way that they are actually sitting on the front half of one of the donkeys and the back half of the other donkey. It also now appears that instead of standing there, the donkeys are now at full gallop!
See https://en.wikipedia.org/wiki/Famous_Trick_Donkeys
Tim shows a few other versions of this puzzle, some of which are different designs including witches on cats and knights on dragons. But then there is a version with three horses (rather than two donkeys) and then some other clever tricks…