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 (Isa 28:27).