I always have trouble choosing just one theme for Halloween so this year each room will have it's own theme! As you already know, the kitchen is the Witch's Lair. Now the living room is being taken over by a Mad Scientist. The inspiration from this particular project came from Dr. Horrible's Sing-Along Blog and it is not only decorative but will provide some of the eerie lighting in this room as well.
I started with some old shipping boxes but you could also use board game boxes or clothing gift boxes. Cut a 1 1/2" border and then cut large holes in the back. I covered the border with packing tape before spray painting it a glossy black. The tape kept the cardboard from soaking up the paint which helped give it more of a glossy finish without having to do multiple coats.
Next, hang push lights on the wall where the holes are. I nailed them in place but if you have some of those 3M removable hanging strips that would be even better. We picked up some push lights at Dollar Tree but they were junk. The springs for the batteries kept bending so it took forever to get them to turn on and even then the intensity of the light varied and some of them stopped working entirely after just a few minutes. We ended up getting better quality ones from Home Depot which were still only about $2.50 a piece.
Tape some waxed paper into the box if there will be gaps between your x-rays.
You can pick up actual x-rays from medical surplus stores or eBay. We already spent $20 just on push lights though and I didn't want to fork over another $30 or more just on this one decoration. So I did a Google image search for "x-ray" followed by names of various bones and printed them out onto regular paper. In the future we might upgrade this prop with real x-rays and frosted plexiglass instead of waxed paper but for now, this gives us the effect we are going for without breaking the bank. :)
This ended up being the perfect size to decorate the shelf above our TV but if you don't have a shelf or mantle, you could just hang the boxes on the wall.