Apparently, a saying was making the rounds at the time: The parents have eaten sour grapes, and the children’s teeth are set on edge (18:2). As the following verses make clear, this saying is a complaint: children are exiled in Babylon for what their parents did (worshiping foreign gods). If the parents were the ones who ate the sour grapes, why should the children’s teeth be on edge? Think of how your jaw locks when you bite into a lemon. Pretty effective metaphor, if you ask me.
