As a reflection of the suggestions, I made a new board, on which you don’t have to hold the clip any more! And you don’t have to keep touching the copper strips on the back of the cards when you insert it. Now there are two modules in the box. One side is connected to the keys on the Makey Makey board. And the other side is connected to ground. When you insert the card, it will connect both sides to form a closed circuit so that certain animation will be triggered.
Since the Max patch is not changed, I will only demonstrate how the new box works in this short video: