Ah, dice stacking. The popular pastime of stacking dice in a cup... Wait, what? You've never heard of it?
Dice stacking is the art of using a cup to stack dice. There is no trick, but a scientific principle, inertia. The dice are first picked up by the cup, and because of the motion of the cup resist movement like a bucket of water swung around. As a result, the dice stack inside the cup and slide around as if they were a single mass.