Example: Heiko has 7 marbles in his hand: 4 red and 3 black. He has 2 blue marbles in his Pool left from his last turn. He places the 4 red marbles and 1 blue marble taken from his Pool on the Potions on his Desk. He wants to keep all the black marbles, so he takes the other blue marble from his Pool back into his hand and places the 3 black marbles into his Pool. Then he ends his turn, and discards the blue marble back into the Dispenser.