Act 2, Sc. 2, lines 173-181: What does he suggest about Hamlet in line 177 (line 177 will be in bold&italics)) that shows to the informed audience that he is not insane?

King. How may we try further?

Polonius. You know sometimes he walks four hours together

Here in the lobby.

Queen. So he does indeed.

Polonius. At such a time I'll loose my daughter to him.

Be you and I behind an arras then.

Mark the encounter: if he love her not,

And be not from his reason fall'n thereon,

Let me be no assistant for a state,

But keep a farm and carters.

King. We will try it.

[Enter Hamlet, reading a book]

Queen. But look where sadly the poor wretch comes reading.

Polonius. Away, I do beseech you both, away.