He esteemeth iron as straw - He regards instruments made of iron and brass as if they were straw or rotten wood. That is, they make no impression on him. This will agree better with the crocodile than any other animal. So hard is his skin, that a musket-ball will not penetrate it; see numerous quotations proving the hardness of the skin of the crooodile, in Bochart.
Related Commentaries of Job 41:27
Job 41:27
27 He esteemeth iron as straw, and brass as rotten wood.