Legendary Australian performance artist Stelarc is known for going to extremes, from aggressive voluntary surgeries and robotic third arms to flesh-hook suspensions and prosthetics. For more than four decades, he's used his body as a canvas for art on the very edge of human experience. He talks with Wired about artists as early warning systems, growing a second skin and the future of his "Ear on Arm" project, in which a partly surgically constructed, partly cell-grown third ear has taken root on his forearm.