I just stumbled upon a discussion of Zener Cards, which I found rather interesting, for several reasons, but mainly because of the obvious point, which never occured to me (probably because I don't spend a lot of time sitting around pondering Zener Cards), that with a deck of 25 cards, 5 of each figure, card counting was a significant factor in experiments with the cards. Apparently some supposed psychics beat Edward Thorpe to the concept of "beating the dealer" by about 30 years (though Thorpe's uses of the skill were more lucrative).