The firemen are gathered in the ship's forecastle. Yank's watch, the men in his work shift, have completed their work and the men gather to rest. All but Yank have showered. The men are unable to fully clean the areas around their eyes, giving them a slightly menacing appearance. In contrast, Yank is still fully covered in coal dust, brooding and hunched over in the position of Rodin's "The Thinker." The men watch Yank carefully, expecting some sort of outburst after his encounter with Mildred. They tease he has forgotten to wash and he remains sullen. They tell Yank the dust will not come off his skin, that it will make him itch and give him spots like a leopard. Insulted, he tells the men to lay off, that he is trying to "tink" and, like always, the men chime, "think!" Yank jumps up and asks them what is wrong with his "tinking?"
Paddy finally decides to speak and suggests that Yank has fallen in love with Mildred. The men repeat Paddy's statement mockingly, shouting "love!" Yank tells the men he has fallen in hate, not love. Paddy informs Yank that only a very wise man could tell the difference between love and hate. Paddy tells Yank that Mildred must love him—after all, why else would she have come into the stokehole? Long jumps up on a bench and cries out that Mildred and the engineers greatly insulted the men. Long asks the firemen what right Mildred and the engineers have to come look at the firemen like animals in a zoo. Long also informs the men that Mildred is the daughter of a millionaire who makes half of the steel in the world and that is why she was able to get into the stokehole. Long then suggests that the men can go to the law for the insult they suffered. Yank replies, "Hell! Law!" The men, in unison, repeat after him, "Law!" Paddy suggests that they go to the governments. In the same pattern, Yank scorns "Hell! Governments!" Again, the entire crew of firemen repeats after Yank, "Governments!" Long frantically suggests that at least God would look at the men equally. Again Yank and the men repeat, "God!" Yank tells Long to join the Salvation Army.
Long gets off the table and Paddy speaks. Paddy bitterly describes the engineer talking to Mildred about the men working, pointing at the workers like animals in the circus. Yank defensively tells Paddy he thought Mildred was a ghost. Paddy once a gain suggests—this time sarcastically—that he could see the kind, loving look in her eyes, just as if she saw a "great hairy ape" escapes from the zoo. Yank is struck by the thought of Mildred calling him a hairy ape. Yank tries to explain that he was just as scared by Mildred as she was by him— he thought she was a ghost. However, the damage is done and no amount of explanation can dispel the insult.
Yank vows to get revenge on Mildred. Yank tells the men that Mildred does not "belong," but the firemen do, all the while his anger escalating. Finally enraged, he madly dashes to find Mildred, but, before he reaches the door, is tackled by the other men. Paddy reminds Yank it is foolish to try to get revenge on Mildred—she has not a real drop of blood in her.
Language and speech distinguish class differences among characters within The Hairy Ape. A character's ability to think and reason is exposed by his speech within the play. The Firemen are immediately identified as less intelligent than Mildred, her Aunt and other higher class characters because they speak in broken and at times incomprehensible utterances. Yank cannot even properly say the word "think," a running joke among the men. In Scene One, Yank himself even laughs at his pronunciation because the word and concept of "thought" is itself a joke—thoroughly unnecessary in the stokehole. Yet, in Scene four the "tink" joke is replayed once again, but Yank reaction has changed. Yank is truly offended by the Fireman's mockery: "Yes, tink! Tink, dat's what I said! What about it?" Mildred's surprise visit to the stokehole has posed a danger that Yank cannot ward off with punches or physical might and thought is suddenly essential.
O'Neill specifically notes that Yank takes on the physical stance of Rodin's sculpture, "The Thinker” during this moment in the play. Although he cannot think, this is his best attempt. He takes on the physical characteristics and interpretation of the quintessential thinker. As Scene Four opens Yank rests in this position while the other men sit about smoking. They look at him "half- amusedly, as if they saw a joke."