Job 40:17

It makes its tail stiff ¹  like a cedar, the sinews of its thighs are tightly wound.

Job 41:23

¹ tn The verb חָפַץ (khafats) occurs only here. It may have the meaning “to make stiff; to make taut” (Arabic). The LXX and the Syriac versions support this with “erects.” But there is another Arabic word that could be cognate, meaning “arch, bend.” This would give the idea of the tail swaying. The other reading seems to make better sense here. However, “stiff” presents a serious problem with the view that the animal is the hippopotamus.