Multistable Objects are perceptual phenomena when unique image can't be recognized from ambiguous patterns.
The most well known is probably spinning dancer illusion which is often erroneously used as brain test to determine whether right or left hemisphere of brain is dominant.
Spinning Dancer Illusion
Spinning dancer silhouette is a bistable illusion where you can see the ballerina move both clockwise and counterclockwise. It is NOT a brain test to determine which part of brain is more used. Let the rotating lady on the right and left guide you (by Nobuyuki Kayahara).
Another classic example is called Necker Cube which was discoverd in 19th century. Is the blue wall in the block or on the block? Is it the back wall or the side wall? You can flip back and forth between the two valid interpretations.
Cube vs 3 Sides
Another variation of Necker's multistable objects is this cube. Is it a perfect cube or just 3 sides of it?
This corner house is a bit tricky. Question: Is the corner concave or convex? Use your palm to cover the upper half of the picture and the corner will be bulged out. However, if you cover the lower half, then it will seem as the inner corner. Amazing.
At first sight, you probably see just 1 face in this Venetian mask. However, there are actually 2 faces - a man and a woman kissing one another. Once you spot them, you will be able to flip between both perceptions of this bistable image. (by 2011 Gianni Sarcone, Courtney Smith & Marie-Jo Waeber)
If you like these brain teasers then feel free to share them with your friends.