Menko Cards
"Menko"s are a traditional folk game played by boys in Japan. Menko cards are basically cardboard cards of a variety of colorful illustration and designs in various size and shape, though rectangular ones and round ones as seen in the image are most common. Players (multiple, no limit) will place their own cards on the ground, and the object of the game is to slap your own card on to the ground and turn over other players' cards by either the air pressure created by the card's being slapped on to the ground, or making the other players' card rebound and turn over by making your card hit another one at the right angle, in which cases you win the turned over card and it becomes yours.
