Boil — To swell, and foam, and froth by his strong and vehement motion, as any liquor does when it is boiled in a pot, especially boiling ointment. The sea — The great river Nile, is called a sea, both in scripture, as Isaiah 11:15, and in other authors, as Euphrates is called the sea of Babylon, Isaiah 21:1; Jeremiah 51:36. Lakes also are most frequently called seas both in the Old and New Testament: and in such lakes the crocodiles are as well as in the Nile.
Related Commentaries of Job 41:31
Job 41:31
31 He maketh the deep to boil like a pot: he maketh the sea like a pot of ointment.