Biting iron and dissolving it with acid

Finally, with a last look of resignation, Barsabbas began to bite at the chains on his wrists. They were thick industrial links. At first the shock of cold metal against his teeth alarmed him, but he worked through the pain and continued to chew at the metal. A Space Marine’s teeth, although heavy and calcified in order to chew indigestible proteins and fibre, could not manage iron. But by the time his calcified enamel was beginning to crack, Barsabbas had mostly lost feeling in his mouth anyway. He salivated, allowing his Betcher’s gland to drool acidic mucus as he worked. He savaged the links at his wrist. Finally the metal, softened by acid, gave way with a snap that split all his remaining molars. Spitting outflakes of iron and fragments of his own teeth, Barsabbas tore his way out of his restraints and began to recouple the power cables to his reactor pack.

 Blood Gorgons pg.151