Jason Kronenwald's Gum Blondes.

Jason has a weird choice of media for his artwork: chewing gum on plywood. From the website:

Each Gum Blonde is 100% chewed bubblegum on a plywood backing. No paint or dye is used. The colour is inherent to the gum - the mixing of colour takes place inside the mouth during chewing using an endless variety of flavours made by an endless variety of companies. Kronenwald has a dedicated team of chewers and prefers the texture of Trident. However, he does not chew gum himself unless he must.

http://gumblondes.com/gb.html (Thanks Yayo!)