Jamieson, Fausset and Brown on Job 41:30

30. stones--rather, "potsherds," that is, the sharp and pointed scales on the belly, like broken pieces of pottery.

sharp-pointed things--rather, "a threshing instrument," but not on the fruits of the earth, but "on the mire"; irony. When he lies on the mire, he leaves the marks of his scales so imprinted on it, that one might fancy a threshing instrument with its sharp teeth had been drawn over it (Is 28:27).