Effect
The magician allows the spectator to select any card, but what the spectator doesn't realise, is the magician is forcing them to pick one card!
Method
There are many, many techniques to do a force. I will only mention one here, one of my favourites as it is nice and easy, and reasonably effective.
The grand-daddy of all forces is the Classic Force, which relies on perfect timing while you spread the cards to leave the force-card under the spectator's fingers at just the right time for them to take it. It is also the hardest, and easiest to go wrong. If you are interested in it, find out how to do it, then use it every time you give a card to a spectator but when you do not need to force it, just for practice. Then when your success rate gets close to 100%, use it for real!
Back to the fan-force. Have the card you wish to force on the bottom of the deck, and start by holding the cards in your left hand, then make a nice fan with them, using your right hand. While you are creating the fan, use your right fingers (which should be below the deck) to pull the bottom card along with you as you create the fan, and leave it about half way under the fan, hidden from view.
Now, run one of your right-hand fingers along the fan and ask the spectator to say stop. When she says stop, split the cards there, making sure that the extra card is held in your right hand, and becomes the bottom card of the top pile of cards that you lift off. Now show them the bottom card (or give it to them).
Voila, you have just forced a card. This is the closest force to the Classic Force that I have found, but with 100% success rate for beginners and professionals.
1. The fan appears normal.
2. Except underneath the force card is in the middle.
3. So when the deck is separated, it becomes the bottom card.
