Donald in Math Magic Club

Try this: Arrange an ordinary deck of cards so that the colors alternate red-black, red-black, all the way through. Now have someone cut the deck as many times as they like. Deal off a stack of cards, one card at a time, that roughly divides the pack in two. Invite someone to shuffle the two stacks together. Then deal cards from the top in pairs. Your audience will be astonished that every pair has a red card and a black card. How can that be?