From the manual...
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Because their skin is made of silicon, the Kran are very resistant to laceration but, lacking flexibility, is more easily damaged by bludgeoning weapons. Silicon still supports oxygen linkages, so Kran breathe much more slowly than other races, enabling them to happily breathe underwater. Without ears, they perceive sounds thanks to vibrations on their bodies. Strong and tireless, Kran are as resistant as the rock that they were born from. Since magic was created to act on different principles, it seems to have little effect on them
Kran metabolism is very complex, they are used to eat sand of various and precious minerals that are digested in their stomach thanks to strong acids. They can also eat food full of mineral salts like seaweed and some crystals created in their kitchen, similar to chemical laboratories.
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They Eat, they breath, and get damaged.
Rats can attack them so they are not that tough and they heal just as fast as everyone else.
The question was do they bleed. and the consensus so far is that they don\'t. Actually I don\'t think any of PS inhabitants bleed.