Ball to square

The magician has one sponge ball. He rubs the sponge ball between his hands and suddenly he has 2 sponge balls. 1 sponge ball, he stops in his left fist, the other in his right fist. After a magical move down two balls in his right hand.

Both sponge balls go back in his fist and when it will open, is a sponge cube in it. The balls have disappeared.

Some training is required.