A Jacob’s ladder (also called magic tablets, Chinese blocks, and klick-klack toy is a folk toy consisting of blocks of wood held together by ribbons.
When the ladder is held at one end, blocks appear to cascade down the strings. This effect is a visual illusion which is the result of one block after another flipping over. It may be considered a kinetic illusion, where the blocks appear to change position when they do not.

Sensory toy for kids.