“I see,” Superman said, nodding. “So Metallo is all three—robot, android, and cyborg.”
“Yes,” Holt agreed, “though I somehow doubt he’s designed for tedious tasks. He’s more cyborg than anything. But from what I could see, the only organic parts of Metallo are his brain and half of his face. And the human brain’s been enhanced. It’s also quite possible that the skin on the human side of Metallo’s face carries some kind of protective coating.”
“What makes you say that?”
“It just makes sense. Why go to all the trouble to build an indestructible cyborg only to leave a big vulnerable patch on its head? Here, look at this…”

Chapter 12