Charles Ellicott Commentary Job 41:30

"His underparts are [like] sharp potsherds: He spreadeth [as it were] a threshing-wain upon the mire." — Job 41:30 (ASV)

(30) He spreads sharp pointed things upon the mire. —Some render, “He spreads, as it were, a threshing sledge upon the mire.” The statement is, that he not only can lie without inconvenience upon sharp-pointed things, but his own body presents a sharp surface to the mud he lies on.