The magician will, with the aid of two decks of cards, demonstrate the impossible;that is, that two solid objects can occupy the same space at the same time!
He takes out two cases that have been pushed together.
He draws a red-backed card from the red case, which he then presents to the audience.
A member of the audience chooses a card from the deck and notes it. The magician replaces the deck in its case, then opens the blue case and takes a blue-backed deck out of it!
Among the blue cards is a red card, which is none other than the card chosen by the member of the audience!