Job 39:16 (ESV)

16 She deals cruelly with her young, as if they were not hers; though her labor be in vain, yet she has no fear,

The ostrich is known for accidentally trampling her young underfoot. When this happens, it seems that she does not even care about the loss. In the ancient Near East, the ostrich was known for its harshness (see Lamentations 4:3).