Below are six cards. Pick one — any one — and remember it. Don't click it. Just hold it in mind.
the method
None of the six cards {{name}} saw is in the second set. Every card changed. The page never knew which one was yours and it didn't need to.
The first set is six picture cards. The second set is five different picture cards. Whichever card {{name}} chose is gone, because all of them are.
first set
second set
Charles Jordan worked the print version of this around 1914. Martin Gardner described it in Mathematics, Magic and Mystery, Dover, 1956. The mechanism is older than that; this is the cleanest form.
round 1