Matthew Poole and continuators on Job 40:21

21. He lieth under the shady trees, in the covert of the reeds, and fens .

For the Elephant being a Creature naturally hot and living generally in hot Countries diligently seeks for and delights shady and waterish places, as is noted by Aristotle and after him by Pliny and Aelian.

o The Elephant lies down to rest himself: and it is but fabulous which some Writers affirm that they have no joints in their Legs and so cannot lie down, but sleep or rest themselves standing or leaning against a Tree. Which is denied and confuted by Aristotle in his History of Living Creatures, 2. 4. and by later Writers.