"Old age is always wakeful. Among sea-commanders, the old greybeards will oftenest leave their berths to visit the night-cloaked deck. It was so with Ahab." In fact, Ahab was spending most of his time on deck, now, and only seldom descending into his cabin. "It feels like going down into one's tomb," -- he would mutter to himself -- "for an old captain like me to be descending this narrow scuttle, to go to my grave-dug berth." So during the night watches, old Ahab would be on deck, but he refrained from stomping on it with his whalebone leg, so as not to disturb the sleep of the mates. But one night, "The mood was on him too deep, and he measured the ship with heavy, lumber-like pace from taffrail (the sternmost rail) to mainmast."
This woke up old Stubb (remember he was Peleg's brother-in-law), who came up from below and "hinted that if Captain Ahab was pleased to walk the planks, then no one could say nay; but there might be some way of muffling the noise . . ."
This was the wrong thing to say, for Ahab responded, "Below to thy nightly grave; where such as ye sleep between shrouds. --- Down, dog, and kennel!"
Stubb, shocked, says, "I am not used to be spoken to that way, sir; I do but less than half like it, sir; I will not tamely be called a dog. sir."
"Avast!" gritted Ahab. "Then be called ten times a donkey, and a mule, and an ass, and begone, or I'll clear the world of thee!"
With that, Stubb retreats down the cabin-scuttle (narrow stairway), muttering that Ahab is the queerest old man he'd ever sailed with. "Is he mad? Not in his bed more than three hours out of twenty-four. A hot old man! I wonder what he goes into the after-hold for, every night?" [The after-hold is a compartment deep below the deck. We will learn that Ahab has secreted there a crew of Parsees (a religious sect of India descended from ancient Persians). It was these shadowy figures that Elijah asked Ishmael about on the Nantucket wharf]. "He might as well have kicked me . . . maybe he did kick me and I didn't observe it. By the Lord, I must have been dreaming . . ."
Resigned, poor old Stubb -- not so "happy-go-lucky" at this point -- gets back in his hammock to finish his night's sleep.