en_tn_condensed/job/41/30.md

him ... he ... His

The words "him," "he," and "his" refer to Leviathan.

he leaves a spreading trail in the mud as if he were a threshing sledge

Just as a threshing sledge goes over grain on a threshing floor and turns it to powder, so Leviathan's tail leaves a trail in the mud as he wags it when he walks. (See: rc://en/ta/man/translate/figs-simile)