I've read a couple of reviews stating the title doesn't make sense within the context of the story. But I'm wondering if its deliberately ironic. I mean, at the beginning the characters begin to believe its an invasion from another country. War is loud and people literally die screaming. In the film, the country (world) is invaded but everyone just dies, as if falling asleep, by the gas.
Just a thought.
'To God there is no zero'