1. A 'predicate' is the part of the sentence that completes its sense. Without it we know only the 'subject,' - the main actor, or the 'object,' the person or thing acted upon, but not what is being said about them.
2. See, e.g.,
Job 21:18: "How often are they like straw before the wind, like chaff swept away by a gale?"
Psm 35:5: "May they be like chaff before the wind, with the angel of Yahweh driving them away"
Isa 17:13: "Although the peoples roar like the roar of surging waters, when he rebukes them they flee far away, driven before the wind like chaff on the hills, like tumbleweed before a gale."
Isa 29:5: "But your many enemies will become like fine dust, the ruthless hordes like blown chaff."
Hos 13:3: "Therefore they will be like the morning mist, like the early dew that disappears, like chaff swirling from a threshing floor, like smoke escaping through a window."