They don't kill you unless you light them. And I've never lit one. It's a metaphor, see
Hazel Grace Lancaster: Really? That's disgusting!
Augustus Waters: What?
Hazel Grace Lancaster: What? Do you think that is cool? Or something? You just ruined the whole thing.
Augustus Waters: The whole thing?
Hazel Grace Lancaster: Yes, this whole thing.
Hazel Grace Lancaster: Even thou you have freaking cancer, you are willing to give money to corporation for a chance to acquire even more cancer? Let me just assure you that not being able to breathe? SUCKS. Totally disappointing. Totally.
Augustus Waters: They don't kill you unless you light them. And I've never lit one. It's a metaphor, see