Notice that the title of this chapter is a stage direction, so we should probably be thinking about ways that the novel is starting to resemble a play.
Also notice that this is the first chapter where Ishmael seems to have completely disappeared as narrator. He’s been fading away for a few chapters now, but in this chapter we don’t get any first-person pronouns, Ishmael doesn’t do anything, and the events in this section, especially Stubb’s monologue, seems to be things that Ishmael couldn’t have witnessed.
The Pequod keeps sailing south and the weather becomes consistently pleasant and beautiful.
Captain Ahab spends more and more time on deck, especially at night. He seems to live on deck and just visit his cabin below, which feels "like going down into one’s tomb" to him (29.2).
At night, when everyone working on deck is trying to be quiet so the others can sleep below, Captain Ahab avoids walking on the quarter-deck (where the captain usually gets to pace around) because the sound of his bone leg would disturb everyone beneath.
One evening, Ahab can’t resist and does start pacing on the quarter-deck. Stubb comes up and tries to suggest that he knock it off, or that perhaps he could put something on the end of his leg to muffle the sound.
Ahab freaks out at Stubb, calls him a dog, and orders him below to his kennel.
When Stubb objects to this, Ahab calls him "a donkey, and a mule, and an ass" and repeats the order to go below decks (29.7).
Stubb heads back down into the ship toward his cabin, shaken and surprised at the way he’s been treated.
At first he just seems angry, but the more he talks about it to himself, the more he appears afraid of Ahab’s bizarre behavior.