I played as a child, and I can see the material of the card from two angles.

It's not a special material, just an ordinary transparent plastic with a special shape, and a specially edited picture is attached below.

As shown in the figure, the cross section of the plastic sheet is a row of semicircles, ready to paste pictures on a straight line (plane); Cut two pictures (a, b) into dozens of thin strips with the same width, reassemble them into a new picture in the order of A 1, B 1, A2, B2, and stick them on the plane of the plastic sheet; In this way, when people look from one direction (A, cyan), they will see picture A composed of some pictures of cyan line segments, and when they look from the other direction (B, red), they will see picture B composed of some pictures of red line segments. This is just a schematic diagram, so the directions of A and B are completely different; In fact, due to the refraction of light by the semi-circular plastic sheet, you can see the two pictures A and B from many angles, but you must have an angle between the two angles to see the picture B before you can see the picture A. In other words, you can see that the angles of the two pictures are separated.