Job 6:5 - Coke's Commentary on the Holy Bible

Doth the wild ass bray when he hath grass, &c.— Grass and fodder here are a figure of abundance and tranquillity, such as the friends of Job enjoyed. To bray and low refer to expressions of grief and uneasiness. Job, therefore, with some smartness, compares his friends to a wild ass exulting in its food, and to an ox perfectly satisfied with grateful pasture; happy themselves, they had not condoled with him in his wretchedness, nor mourned with him, but rather blamed his mourning as importunate clamour, and as if he had behaved himself towards God with insolence and impatience. Schultens.