DIY Bokeh modification

I don't understand how but these construction paper lens caps change the shape of the bokeh into whatever shape you want. I cut the shape of a tree and a dog bone or dog treat here to give this a try.

 

here are some web sites:

 

www.mcpactions.com/blog/2010/12/02/how-to-photograph-star...

 

www.diyphotography.net/diy_create_your_own_bokeh

Done