OET interlinear JOB 41:24

uW Translation Notes:

Note 1 topic: figures-of-speech / metaphor

לִ֭בּ⁠וֹ יָצ֣וּק כְּמוֹ־אָ֑בֶן וְ֝⁠יָצ֗וּק כְּ⁠פֶ֣לַח תַּחְתִּֽית

his/its=heart hard (Some words not found in UHB: his/its=heart hard as_~_as stone and,[it_is]_hard like,a_mill-stone lower )

Here the would heart could mean: (1) the disposition of Leviathan. If that were hard, then Yahweh would be saying that Leviathan acted cruelly and was not afraid of anyone or anything. Alternate translation: [It acts cruelly and fears nothing]; (2) the chest of Leviathan. Alternate translation: [Its chest is hard like stone; yes, it is hard like a lower millstone]

Note 2 topic: translate-unknown

כְּ⁠פֶ֣לַח תַּחְתִּֽית

(Some words not found in UHB: his/its=heart hard as_~_as stone and,[it_is]_hard like,a_mill-stone lower )

A millstone is one of a pair of large, flat, round stones that people use to crush kernels of grain to process them into food for humans. The lower millstone needs to be especially strong and hard because it bears the weight of the upper millstone and the force of the crushing. If your readers would not be familiar with what a millstone is, in your translation you could use the name of a comparable object in your culture or you could use a general expression. Alternate translation: [like a stone that people use to crush grain]