Rotation changes the interpretation

From Michael’s “Visual Phenomena & Optical Illusions”

Some things change completely when turned upside down. In the neighbouring movie you may observe: the beaver (or water rat?) changes to a donkey.

You can run / pause by clicking the top left button. You can also click on the slider and rotate manually, or use the left-right cursor keys after clicking on the slider handle.

Source

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

In the fairy tale at the left, bistable situations can occur at oblique angles. You can test this using the bottom slider.

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”.

The above 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 ;-)).