Adam Clarke on Job 38:40

When they couch in their dens - Before they are capable of trusting themselves abroad.

Abide in the covert - Before they are able to hunt down the prey by running. It is a fact that the young lions, before they have acquired sufficient strength and swiftness, lie under cover, in order to surprise those animals which they have not fleetness enough to overtake in the forest; and from this circumstance the כפירים kephirim, "young lions, or lions' whelps," have their name: the root is כפר caphar, to cover or hide. See the note on Job 4:11, where six different names are given to the lion, all expressing some distinct quality or state.