- Given the way that the curse spreads, wouldn't the whole human race be wiped out after a few years?
- Yes. That is the threat. Kayako isn't your average ghost in haunted house, she's like a Kishin Egg or Alucard because her mother used her as the can to seal evil spirits and demons in and Takeo's murdering her unleashed that evil, but she was sealed in the Saeki House until Karen burned it. If her sister didn't show up in the third film, you would be seeing a Kairo/Pulse-level of Apocalypse How (I was actually expecting that), from Class 1: Human Die-Back to Class 2: Civilization Extinction, since her curse spreads like The Virus, from a person entering her house to anyone in the vicinities of said person, and anyone in the vicinities of THAT person and so on. They didn't outright say it in the movie, but it's quite likely that hospital Karen stayed at, Eason's apartment, that motel Miyuki went to, the phone booth Vanessa was taken by Kayako and Kayako's mom's house are also cursed, so every doctor, nurse, patient and visitor from that hospital, every person living close to Eason, everyone who goes in that motel and that phone booth(and likely the high school) and everyone who passes by Kayako's mom's house will also be cursed, not to mention the firemen and policement that rescued Karen from the fire, at least a few dozen men. Do the math. If Kayako wasn't so slow in her movements and retained actual sentience to coordinate the people she consumes, she could have easily killed mankind in a year, if not a few months.
Headscratchers / The Grudge