So simple - yet so difficult. This old-fashioned optical illusion trick has been a hit since it arrive. In fact, our family bought the entire first batch! Each arrives in a printed envelope ready to amaze and mystify your friends. The solution is folded in a tiny envelope.
But, don't open it right away, try to master it first. Engineers and artists alike will enjoy the elegant solution that is certainly not immediately obvious.
Warning: Buy several: you'll find yours missing in record time!