King James Version (KJV)
Sharp stones are under him: he spreadeth sharp pointed things upon the mire.
Modern English
His underparts are like sharp potsherds; he spreads himself like a threshing sledge on the mire.
Hebrew
תַּ֣חְתָּיו חַדּ֣וּדֵי חָ֑רֶשׂ יִרְפַּ֥ד חָ֝רוּץ עֲלֵי טִֽיט׃
taḥtayv ḥadvdey ḥares yirpad ḥarvṣ ʿaley ṭiyṭ