Some things change completely when turned upside down. Place your mouse over the neighbouring image, it begins to rotate. You may observe: the beaver (or water rat?) changes to a donkey.

Source

Julian Jusim: “Kopfunter/Kopfüber” (Jusim/Pressler, Hanser-Verlag)

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In the “fairy tale” at the left, bistable situations can occur at oblique angles. You can test this by stopping at the right instant.

Source. I constructed this movie from the picture “a-j-a.gif” which I found “somewhere on the Internet”. It is also known as “(after) 6 beers”. Could anyone enlighten me about the original source? [It’s not from the “Invisible Monsters” cover, I had this image before that book came out.]
The painter Rex Whistler created a similar design “Cinderella and her fairy godmother”.

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The top picture has been embodied in this very neat coin design (The “Hillary Illinois Quarter”) on the right, which can actually be obtained at Joel’s Coins (for a little more than a quarter ;-)).