Sponge Balls with Jumbo Climax

Two sponge balls are shown. The magician puts one in his pocket and the other in a spectator's hand. With a magical gesture, the ball in the magician's pocket disappears, and ends up in the surprised spectator's hand, that now has two balls.
The same effect is repeated for three times, in different ways.
To end the routine, the magician puts two sponge balls in the spectator's hand, and instantly they  transform into a large ball!

• The balls have a diameter of 4 cm and the jumbo ball of 8 cm.