Cassio returns with Montano, the governor of Cyprus, and a number of unnamed "gentlemen".  Immediately Iago, undeterred by Cassio's queasy concern that "they have given me a rouse already", launches the drinking party by calling for wine, and singing.  Cassio — already beginning to feel the elation of wine — appreciates Iago's song  immoderately: "Fore God, an excellent song!"  Iago explains, in lines which one can readily imagine being greatly appreciated in the Elizabethan playhouse, that he learned the song in England, "where indeed they are most potent in potting. Your Dane, your German, and your swag-bellied Hollander — drink, ho! — are nothing to your English."  Cassio is bemused: "Is your Englishman so exquisite in his drinking?" (One of the subtle ways in which Shakespeare dramatised Cassio's descent into intoxication was by making him repeat the word "exquisite" three times in little more than 70 lines of this scene.) 

Iago, now in full, feigned, bonhomous flight, praises the Englishman's capacity to hold his drink in lines which again must have set the playhouse in a roar: "Why, he drinks you with facility your Dane dead drunk; he sweats not to overthrow your Almain; he gives your Hollander a vomit ere the next pottle can be filled."

Infected by Iago's pretence of camaraderie, Cassio picks up the mood and pledges a health to Othello, thus for the first time taking the lead in drinking. It marks the turning point from exuberance into confusion, befuddlement, and repetition. Asked by Iago if he would like him to sing again, Cassio's reply comes from a man whose wits are about to be overcome by the fumes of wine: "No, for I hold him to be unworthy of his place that does...those things. Well, God's above all, and there be souls must be saved, and there be souls must not be saved." 

From here it is for Cassio only a small descent to the familiar litany of the truly drunk: "Do not think, gentlemen, I am drunk: this is my ancient, this is my right hand, and this is my left. I am not drunk now: I can stand well enough, and I speak well enough." Then the scene degenerates swiftly into a brawl, as Cassio fights first with Roderigo, whom he has encountered off-stage, and then Montano, whom Iago has told that Cassio is an habitual drunkard, and who says the one thing calculated to infuriate anyone who has had too much to drink: "Come, come, you're drunk."

Shakespeare is good at drinking scenes, and a number of plays are enlivened by drunks on stage — for instance, Henry IV, Tempest, Macbeth, and Antony and Cleopatra. But the scene in Othello is not just beautifully observed. The significance of Cassio's intoxication and of Iago's entrapment of him is deepened by being played out against the background of Othello's wedding night.