"A thaumatrope is an optical toy that was popular in the 19th century. A disk with a picture on each side is attached to two pieces of string. When the strings are twirled quickly between the fingers the two pictures appear to blend into one due to the persistence of vision." (Wikipedia)

In 1824, Peter Marc Roger discovered the important principle of vision stability, and this is the principle that the eye retains any image it sees for a short time!
This principle led to the emergence of a series of devices that are mostly entertainment, which are actually among the first two-dimensional animations, such as:
Thaumatrope: A cardboard sheet that was placed between two pieces of thread and a cage was painted on one side and a monkey or bird on the other. When you swing the threads, the images merge and it looks like a monkey or a bird in a cage.

I have designed 9 animal and bird characters that appear with different layers in the background and the other side of the thaumatrope, which is a cage or farm, is combined with them.
Have you made this nostalgic toy yet? You can have a NFT of that!