In my urban fantasy, I follow a race of magical creatures that can eat metal. They are made, not born, by forming their body and using an incantation to animate them. They are made of clay, have bones made of stone, big sharp teeth that allow then to rip through metal, and they look a little like Gollum from LotR. They can walk on all fours, but they mostly walk upright. They can also shapeshift to look human, using whatever face they desire. I thought about giving them claws to help them climb (they help clean up war damage by climbing buildings and eating them.. lol), but I haven't decided yet. I also debated giving them poisonous blood, but I worry that with the claws, teeth, and shapeshifting, they have enough ways to protect themselves. My problem is... I don't know how readers are going to handle it. The concept behind the metal was that, since they're made of clay, the metal they eat breaks down and merges with their body, keeping their clay form refreshed. But I'm not a scientist. And I don't know how believable that is. Is this too far fetched? Should I change what they eat? My entire story revolves around them, so I'd hate to get all the way to the end and have to change it. Thoughts? Suggestions?