Sharp stones are under him; rather, jagged potsherds are under him; i.e. "his belly is covered with jagged scales"—a thing which is true of the crocodile, but scarcely of any other beast. He spreadeth sharp pointed things (rather, a threshing-wain, or a corn-drag) upon the mire.
He leaves on the mud on which he has lain, i.e.' an impression as of an Oriental threshing-wain, or corn-drag, which is "a thick plank of timber, stuck full on the under side, of flints or hard cutting stones arranged in the form of the palate or rough tongue of a cow".
The mud-banks on which crocodiles have been lying are said to be scored all over with such impressions.