When I was a child I used to have a lenticular ruler. A 12 inch strip of flexible plastic with pictures of dinosaurs. When you moved it from side to side the dinosaurs raised their heads, walked to the left, munched on some leaves or attached an unwitting victim. It would keep me amused for ages and it is a proven scientific fact* that males of all ages are magnetically attracted to anything that displays a lenticular effect.
Technology has since taken lenticular engineering to new heights and it isn’t just rulers nowadays, oh no, you can get huge advertising billboards that appear to move as you walk past them. You can usually spot these from a distance due to the number of adult males moving repeatedly backwards and forwards in front of them.
The way lenticular images work is by splicing two or more pictures together and arranging them in sequence behind a screen of prisms (usually just shaped plastic). The prisms refract the light so that the viewer can only see one complete picture at a time, but as the object moves through the field of vision, the other images slowly appear and create an animation effect.
*Of course it isn’t, but I bet I’m right.