I love brain teasers and wood-based puzzles and this is a good one that you can easily make yourself. Basically, all you need is a chunk of pine, a nail, and some boiling water (oh, and a saw and a drill).[youtube:http://youtu.be/fEATei2wewY]
It’s called the “Tooth and Nail” puzzle, and it appears to be an optical illusion. It is not.
SPOILER ALERT: How this works is fascinating. After three sections are cut from the wood, one of the remaining “teeth” on the end of the puzzle is saturated in boiling water. This allows the soft pine wood to be significantly compressed enough so that a hole can be drilled through the two center teeth to accept a nail. As the wood on the compressed tooth dries, it returns to its original shape and the illusion is complete.