Lip window

This is certainly a remarkable body modification (click to enlarge photo).

I couldn't bring myself to track down the backstory at the sites watermarked on the photo, but as best I can tell from reading the discussion thread at Reddit, this is a Pyrex plug; presumably refraction of transmitted light explains the visualization of both top and bottom teeth through the plug.

Update:  While I was writing this post, I kept thinking that this modification reminded me of something, but I couldn't remember what it was.  Last night it came to me - the "Futches Reich" postal forgery produced during WWII for Operation Cornflakes (third stamp below, click to enlarge):

Some people refer to it as the "Hitler zombie" stamp.  Philatelists will already be familiar with it; others interested in reading about it should go to this outstanding website on propaganda and espionage philately.