I just realized something fairly subtle about this scene the other day. This is Claudius after the nunnery scene above:
"Love! his affections do not that way tend;
Nor what he spake, though it lack'd form a little,
Was not like madness. There's something in his soul,
O'er which his melancholy sits on brood;
And I do doubt the hatch and the disclose
Will be some danger..."
Now, on the one hand, this is partially wrong: Claudius has just seen incontrovertible proof that Hamlet's feelings for Ophelia ARE motivating his distemper. On the other hand, he is also correct: strictly speaking, Hamlet's display is one of anger, not affection, and that anger -- odd because it accuses Ophelia of things that we know that Hamlet is upset at his mother for -- is apparently genuine. Finally, Claudius' words, I believe, are given an extra sense of rightness by another system at work: the irrational (but nonetheless substantive) connection between "sits on brood" and "hatch" on the one hand and "melancholy" and "brood" on the other.

A similar irrational system operates in the next scene as well:
HAMLET. O good HORATIO, I'll take the ghost's word for a thousand pound. Didst perceive?

HORATIO. Very well, my lord.

HAMLET. Upon the talk of the poisoning?

HORATIO. I did very well note him.

HAMLET. Ah, ha! Come, some music! come, the recorders!
For if the king like not the comedy,
Why then, belike, he likes it not, perdy.
Come, some music!