1，filling the plastic cup with rice grains;
2, compacting the rice grains already in the cup with your hand;
3, pressing the rice grains with your hand, and inserting a chopstick between your finger gap;
4, hoisting the chopstick slowly with your hand; the cup and rice grains can be lifted together.
Given the pressing force among rice grains, air inside the cup would be squeezed out. The external pressure is larger than that inside the cup, bonding chopsticks and rice grains closely. That's why the plastic cup full of rice grains can be hoisted by a chopstick.