The Hydra is the many-headed monster whom Hercules slew in the second of his twelve labors (see page I-237).
Iago, however, has the cure for Cassio's pessimism and pulls another string. All Cassio need do is ask Desdemona to intercede with Othello, and he can reach Desdemona through her lady in waiting, Emilia, who happens to be Iago's wife. With the dawn of hope, Cassio agrees to try.
... the green-eyed monster. ..
The plan begins well. Cassio sees Emilia and then Desdemona, and the latter agrees to intercede with Othello.
As Cassio leaves Desdemona, however, Iago and Othello arrive on the scene and Iago, looking after Cassio, mutters:
Ha! I like not that.
- Act III, scene iii, line 34
He won't explain himself, but it is enough to insert the first uncertainty into Othello's mind concerning Desdemona and Cassio. Then, when Desdemona begins to plead for Cassio, that can but increase the uncertainty.
After Desdemona leaves, Iago, with infinite cleverness, manages to fire Othello into jealousy by the very manner in which he himself refuses to say anything. The very show of reluctance on Iago's part gives Othello the greater room for imagining the worse, and Iago warns him in terms that but feed his fear, saying:
O, beware, my lord, of jealousy!
It is the green-eyed monster, which doth mock
The meat it feeds on.
- Act III, scene iii, lines 165-67
Because of these verses, the expression "green-eyed monster" has become a common metaphor signifying jealousy and its mundane meaning is lost. The "green-eyed monster" is obviously the cat, which plays with the mouse it catches, releasing it only to catch it again, over and over. In the same way, jealousy torments the one who experiences it, for he cannot ever be made secure. Every proof to the contrary releases him only briefly, till some new incident rouses the jealousy again.
... her jesses...
Othello understands the torments of jealousy and he will not sit still to be a prey to it. He will have the matter put to the test, either to be proven or disproven. After Iago has left, he muses:
// I do prove her haggard,
Though that her jesses were my dear heartstrings,
I'd whistle her off and let her down the wind
- Act III, scene iii, lines 259-61
The language used here is that of falconry. In medieval times it was an aristocratic sport to train falcons, hawks, and other birds of prey to hunt game, and, like every other specialized activity, it developed its own vocabulary.
A haggard is an untamed hawk; one that is caught after it is adult so that any taming is superficial and so that there always remains a tendency to revert to the wild. Jesses are small leather straps around the hawk's leg which are usually supplied with a ring that can be attached to the glove on the hawker's hand. To whistle her off would be to let her go.
Actually, though, Othello is already convinced of Desdemona's infidelity. When she comes in to call him gaily to dinner, she sees something is wrong and asks if anything ails him. He answers, ominously:
/ have a pain upon my forehead, here.
- Act III, scene iii, line 283
He touches his forehead, and to the Elizabethan audience, any reference to the forehead means the horns that sprout there and signify cuckoldry.
The innocent Desdemona offers him her handkerchief to bind his head but he pushes it roughly away and it falls to the ground unnoticed by her.
The handkerchief is a very special one, a gift to Desdemona from Othello. Now it lies there and Emilia picks it up. Her husband, Iago, had often asked her to steal it for him (we are not told why) and now she can give it to him.
Iago is elated on receiving it. He sees how he can use it in his plan. When Othello enters, Iago muses with grim satisfaction on the perturbed appearance of the general. He says to himself, concerning Othello:
Not poppy nor mandragora,
Nor all the drowsy syrups of the world,
Shall ever medicine thee to that sweet sleep
Which thou owedst [possessed] yesterday.
- Act III, scene iii, lines 327-30
There has always been a use for the equivalent of tranquilizers, for there have always been tensions. Before the days of modern chemistry, tranquil-izing herbs were found in nature, and of these the chief was a certain species of poppy which was originally grown along the shores of the eastern Mediterranean for the sake of its edible seeds.