C. F. Keil and Franz Delitzsch on Proverbs 19:12

Pro 19:12 12 A murmuring as of a lion is the wrath of the king,      And as dew on plants is his favour.

Line 1 is a variation of Pro 20:2; line 2a of Pro 16:15. זעף is not the being irritated against another, but generally ill-humour, fretfulness, bad humour; the murmuring or growling in which this state of mind expresses itself is compared to that of a lion which, growling, prepares and sets itself to fall upon its prey (vid., Isa 5:29, cf. Amo 3:4). Opposed to the זעף stands the beneficial effect of the רצון, i.e., of the pleasure, the delight, the satisfaction, the disposition which shows kindness (lxx τὸ ἱλαρὸν αὐτοῦ). In the former case all are afraid; in the latter, everything lives, as when the refreshing dew falls upon the herbs of the field. The proverb presents a fact, but that the king may mirror himself in it.