The mood throughout The Hairy Ape is tense, with various characters expressing their disparate views on class, race, industrialization, and progress, among other things. The frequent clashing of these characters contributes to the tense mood, representing the conflict between young and old or rich and poor in a rapidly shifting, progressing modern world.
One such clash occurs between Yank and Mildred in Scene 3, shifting the mood from triumphant—as Yank's outlook has been thus far—to frustrated, or, at its worst, despairing.
MILDRED: [About to faint—to the ENGINEERS, who now have her one by each arm—whimperingly] Take me away! Oh, the filthy beast!
[She faints. They carry her quickly back, disappearing in the darkness at the left, rear. An iron door clangs shut. Rage and bewildered fury rush back on YANK. He feels himself insulted in some unknown fashion in the very heart of his pride. He roars]
In this scene, Yank's confidence and pride as a working man are undermined by Mildred's referring to him as a "filthy beast." While Yank has felt a kind of righteous fury against the bourgeoisie before, he has not yet felt humiliated fury. This emotional and psychological shift accompanies a mood shift within the text.