With the bones held in the proper position... snap the wrist either inwards or outwards in a quick but gentle motion. When done properly you will get a single clear snap.

Important! You do not manipulate the bones like chopsticks. The bones stay in a fixed position. It is the motion of the wrist and forearm that make the bones snap.

If you are holding the bones properly, they snap with the motion of the arm... it has to work.