Another neat DIY project!
I like the results but I am having a hard time figuring out the setup????
You pop the flash into the box...seems a bit confusing. Does the flash make the effect or the camera itself.
I guess I gotta try it to find out.
Use Light Stencils To Create Amazing Light Paintings | DIYPhotography.net

Here's a link to more work and examples on Flickr:
Light Stencils - a set on Flickr