Look at the 2 pieces of wood and you will clearly see 13 horizontal lines.
Yet flip the frame upside down and there are only 12 lines! How can this be?
My son calls this the "Sobriety Test", yet there is an interesting math basis for the puzzle which is explained in the video.
It is a wonderful illusion that I got the idea to make from one of Martin Gardner's recreational math books. Good for messing with friends, or a coffee table/bar type item, or effective in the math classroom also.
Pieces are made from 1/4" thick hardwood, either maple or cherry. Base is made from floorboard material so is very strong. Size of puzzle in base is 7" x 3.25" x .6"
Level of Difficulty: Level 2