Wooden Illusion

I found a picture of this online but couldn't find the instructions on how it was built. With some trial and error, I recreated the illusion.

Watching the video is the easiest way to see how it works. I've included a drawing which is linked in the video description.

https://www.youtube.com/watch?v=b3vbaZP2cL8

Build Instructions:
http://www.instructables.com/id/Wooden-Illusion/