Migraineman writes "I stumbled upon a clever hack by Sprite. He reverse engineered the pin functions on an HP inkjet cartridge, and built a simple driver board that converts the cartridge into a hand-held inkjet printer. The driver board is programmed with a fixed message. Moving the "print head" is your responsibility, but it leads to some interesting applications. Printing messages on a whiteboard was the original inspiration, but printing messages on the foam head of a Guinness is just inspired."