The magician shows a red foam ball, which he pushes into his fist. He closes both fists and asks the spectators which hand the red ball is in.
It doesn't matter what the answer is, because if you open one of his hands, you'll find a BALL BLACK, and in the other hand, it's a coloured CUBE. RED that we see appear ! !
The red ball is in the pocket!
That's easy to do.