double doors for pop-up cards

Now for the words. For whatever it's worth.

A hinge is placed on one side near the central fold. When the card is flat, both card and hinge are flat. When the card is opened the hinge travels from one side of the central fold to the other side of the central fold in an arc. The distance the hinge moves is the movement affected on the other side. The hinge becomes a piston moving back and forth by the card opening and closing. The energy of the back and forth piston is manipulated to flip two doors. The doors drag with them monkey-arms making it appear as if the monkey is opening the doors and not the doors pulling the monkey's arms.