Iago was artful, and had studied human nature deeply, and he knew that of all the torments which afflict the mind of man (and far beyond bodily torture), the pains of jealousy were the most intolerable, and had the sorest sting. If he could succeed in making Othello jealous of Cassio, he thought it would be an exquisite plot of revenge, and might end in the death of Cassio or Othello, or both; he cared not.
The arrival of the general and his lady in Cyprus, meeting with the news of the dispersion of the enemy's fleet, made a sort of holiday in the island. Every body gave themselves up to feasting and making merry. Wine flowed in abundance, and cups went round to the health of the black Othello, and his lady the fair Desdemona.
Cassio had the direction of the guard that night, with a charge from Othello to keep the soldiers from excess in drinking, that no brawl might arise, to fright the inhabitants, or disgust them with the new-landed forces. That night Iago began his deep-laid plans of mischief; under cover of loyalty and love to the general, he enticed Cassio to make rather too free with the bottle (a great fault in an officer upon guard). Cassio for a time resisted, but he could not long hold out against the honest freedom which Iago knew how to put on, but kept swallowing glass after glass (as Iago still plied him with drink and encouraging songs), and Cassio's tongue ran over in praise of the lady Desdemona, whom he again and again toasted, affirming that she was a most exquisite lady: until at last the enemy which he put into his mouth, stole away his brains; and upon some provocation given him by a fellow whom Iago had set on, swords were drawn, and Montano, a worthy officer, who interfered to appease the dispute, was wounded in the scuffle. The riot now began to be general, and Iago, who had set on foot the mischief, was foremost in spreading the alarm, causing the castle-bell to be rung (as if some dangerous mutiny instead of a slight drunken quarrel had arisen): the alarm-bell ringing awakened Othello, who, dressing in a hurry, and coming to the scene of action, questioned Cassio of the cause. Cassio was now come to himself, the effect of the wine having a little gone off, but was too much ashamed to reply; and Iago, pretending a great reluctance to accuse Cassio, but as it were forced into it by Othello, who insisted to know the truth, gave an account of the whole matter (leaving out his own share in it, which Cassio was too far gone to remember) in such a manner, as while he seemed to make Cassio's offence less, did indeed make it appear greater than it was. The result was, that Othello, who was a strict observer of discipline, was compelled to take away Cassio's place of lieutenant from him.