Joining in on a fool's folly when answering him represents answering him in a foolish way. AT: "Answer a fool according to his folly" or "Answer a fool foolishly"
The eyes represent seeing, and seeing represents thoughts or judgment. AT: "so that he will not become wise according to his judgement" or "so that he does not consider himself to be wise" (See: [[rc://en/ta/man/translate/figs-metaphor]])