This will work with regular playing cards as well as the
larger sizes of Tarot Cards. However, since we have a large
number of magicians now reading The Wizards' Journal, we'll show
how to do the effect with regular playing cards and assume the
Wizards can adapt it to the larger Tarot brands.
After doing some standard Tarot reading stuff (with either
Tarot or normal playing cards), I have someone slide a card to
the edge of a table and I hand the person a sharpie pen to make a
mystic symbol on the front of the card, and perhaps put their
initials or a nickname on the card as well, so the "spirits
will know whom to blame."
As they do so, I bring out a tiny wooden jewelry box (craft
store) and set it next to the deck so they can see how small it
is in comparison to the normal sized cards. I ask the person to
look at the card she has chosen (I almost always pick a woman for
this effect because I like they way they scream at the ending!).
Then I ask her to mix her card back into the deck and put the
entire deck of cards into the tiny wooden box. Of course, this
seems impossible, but then I take the deck and squeeze it,
shrinking it down to a tiny deck of cards which just fits into
the small box. I hand her the wooden box and ask her to hold it
while I go on to something else. Every once in a while, I ask her
if she still has my cards because I will need them later. She
answers "Yes" and I continue with some other
demonstration or trick.
Finally, I ask her to dump the card deck into my hand. I hold
out my hand and when she opens the box, all that is inside is one
single tiny card... the one she chose. When she turns the card
over, she sees that whatever she wrote on the large card is still
there in her own handwriting, but it has all been shrunken along
with the card.
That's usually when she starts screaming. I let her keep the
card as a souvenir after I affix a sticker with my name and phone
number.
There is no need to force a card, since she is
going to write on the face of the card and therefore might as
well have a perfectly free choice.