When Jacob stops by his house on the way to the Cullens' place, Billy senses Jacob's plans. He asks his son to leave Bella and the Cullens alone. But Jacob races on his motorcycle toward the Cullen house, dead set on killing Edward and as many of the other Cullens as possible.
To his surprise, when Jacob reaches the Cullen house, he sees Bella is still a human. She does look very sick, though. "There were deep circles under her eyes… her face was haggard…a sheen of sweat covered her skin…" (9.86). He's confused to see that Rosalie seems to act as Bella's bodyguard, because Rosalie never liked her before. Edward, meanwhile, looks "tortured."
When Jacob presses Bella for answers, she reveals her pregnant body. Jacob is horrified:
I didn't want to see this…didn't want to imagine him inside her… because whatever was inside her was taking her life to feed its own. (9.115-116)
Edward asks Jacob to step outside. Jacob's hate for him subsides at the sight of Edward's pain. "This was the face a man would have if he were burning at the stake" (9.138). Edward confirms that "the thing" inside of Bella is killing her, but that Bella won't abort it. Rosalie is acting as her bodyguard.
To convince Bella to give up the baby, Edward presses Jacob to offer to make a baby with her instead, since he's not a vampire. Jacob admits to himself that it sounds "so messed up," yet "so tempting."
He doesn't really think Bella will go for it. He agrees to try, though. In turn, Edward promises that Jacob can kill him if they fail to convince Bella and she ends up dying from giving birth.