The Fortune Teller Fish works based on simple physical and chemical principles involving moisture absorption. It is made from a very thin piece of cellophane or a similar hygroscopic polymer material, such as sodium polyacrylate, which is capable of absorbing water molecules from the moisture on your skin
. When you place the fish on your palm, the side of the fish touching your skin absorbs moisture (sweat) and expands. This expansion causes the fish to curl, wiggle, or even flip over. The movement occurs because only one side of the fish swells while the other side remains dry, creating a bending effect due to the difference in expansion between the two sides
. The direction and type of movement depend on the orientation of the polymer strands (the "grain") in the fish material. For example, if the polymer strands run head-to-tail, the fish curls in that direction; if they run side- to-side, the curling follows that orientation
. The fish does not respond to heat alone; experiments show that placing the fish on a hot dry surface does not cause movement, confirming that moisture absorption—not temperature—is responsible for the effect
. In summary, the Fortune Teller Fish "moves" because it is a moisture- sensitive polymer that swells unevenly when exposed to the humidity of your skin, causing it to bend and twist in various ways. The movements are often interpreted as "fortunes," but this is purely for entertainment, with no real predictive power
