You need an SWF block, a red block with a white F and a white block with a red F and then you'll see what it does :)
Can't be sold, but is kind of funny and gives some xp, so worth holding onto :)
There are three parts -- one is SWF on what looks like a little self-inking stamp, one big red f, and the other one I've never seen because as soon as I get it the three parts come together to make what looks like a GLITCH game box. Then your glitch can play Glitch. You can't sell the individual components and I've only gotten them from petting pigs. It's kinda cool, but it breaks really quickly. Never enough time to play Glitch. :)