Two Way by Kreis Magic - Trick

Effect

A metal box is displayed. There is a prediction inside. Two decks are placed on a table. One is red-backed, and the other is blue-backed. A spectator chooses either of them (not a magician's choice). The magician takes the chosen deck, and mixes the cards well. Some cards become face up, and the others face down. The cards are spread on the table. The magician removes all the face-down cards to leave the face-up cards only. The remained face-up cards are given to the spectator. Then spectator does the same as the magician did. This is repeated until one face-up card is left. When the box is opened, there found a chip having the same suit and value as that of the remained card.