Card-guessing tricks give a magician the opportunity to show off his or her mind-reading prowess. In many cases, the illusion of mind reading arises not from sleight of hand but as a consequence of some mathematical principle.
One of the most startling of such prediction tricks is known as the Kruskal count, named for Rutgers mathematician Martin D. Kruskal.
The magician invites a subject to shuffle a standard deck of 52 playing cards, then secretly pick a number between 1 and 10.