What if this exchange were a vaudeville routine wherein Polonius is playing the straight man? As if Hamlet said, “My wife is so mean.” And Polonius said, “How mean is she?” which would lead Hamlet right to the punchline. Ba dum bum.
Because the answer to what treasure Jephthah had might seem obvious if you know the story and one would assume Polonius might know the story. Or perhaps he doesn’t – maybe Polonius is an expert in the ancients but not a religious man and Hamlet is a bit more Judeo-Christian?
Or Polonius could just be humoring Hamlet the way you do a child or a crazy person. But somehow I enjoy the idea of a little Polonius/Hamlet repartee.